UNIVERSITY  OF  CALIFQHBIA 

DEPAKTLIBTT  OF  CIVIL  ENGINEERING 
STRUCTURAL  ENGINEERING. 


NOTES  ON  FOUNDATIONS  AND  MASONRY  STRUCTURES 
COURSES  C.   E.   113  -  114 

By 
Charles  Derleth;  Jr. 


Revised  and  Enlarged  From  Earlier  Mi t ions 
Berkeley,  California,   October  1,1921. 


DESIGN 


OF  A 


RAILWAY  BRIDGE  PIER 


BY 

CHARLES  DERLETH,  Jr.,  C.  E. 

Associate  Professor  Structural  Engineering 
University  of  California 


NEW  YORK 

THE  ENGINEERING  NEWS  PUBLISHING  COMPANY 
1907 


Engineering 
library 


PUBLISHERS  NOTE. 

The  following  study  was  prepared  by  Professor  Derleth  at  the  request  of  the 
editors  of  the  California  Journal  of  Technology,  and  printed  in  the  November 
(1906)  number  of  that  magazine. 

It  is  believed  that  this  article  covers  the  subject  of  bridge-pier  design  in  a 
more  complete  and  efficient  manner  than  any  text  now  extant,  and  recognizing 
its  value,  especially  to  students,  it  has  been  thought  advisable  to  reprint  it  in 
the  present  permanent  and  available  form. 


Design  of  a  Railway  Bridge  Pier. 

By  CHARLES  DERLETH,  Jr.,  C.E. 


I.  INTRODUCTION. 

1.  Senior  students  in  the  College  of  Civil  Engineering  of  the  University  of 
California   design   completely   the  metal  superstructure  for  an  inclined  upper 
chord,  double-track   railway  bridge,  usually  about  300  ft.  in  span  length.     This 
article  attempts  to  give  the  calculations  for  a  first  study  of  an  intermediate 
pier  to  carry  a  superstructure  like  that  designed  by  our  senior  students.     A 
foundation  is  selected  of  a  depth  not  too  great  to  properly   employ   the  pneu- 
matic process.     The  pier  is  assumed  to  rest  on  a  rock  and   the  caisson  proposed 
is  of  steel. 

2.  The  pier  from  the  coping  to  the  caisson  roof  is  not  designed  in  detail,  but 
only  in  general  proportions.     Its  outlines  are  proposed  and  the  general  type  of 
construction  at  different  levels  is  clearly  indicated ;  the  article  in  these  particulars 
attempts  to  show  merely  that  the  proportions  assumed  give  a  pier  which  satisfies 
all  practical  considerations,  is  economical  and  of  good  appearance,  and  that 
it  is  stable  when  subjected  to  the  worst  combinations  of  external  loads  and  forces. 

3.  A  purely  ideal  case  and  fictitious  foundation  site  have  not  been  assumed. 
In  order  to  give  added  interest  to  the  problem,  the  calculations  are  based  upon 
conditions  found  for  Pier  8  of  the  Havre  de  Grace  Bridge  of   the  Baltimore  & 
Ohio  Railroad.      (Consult  Fig.  1,  Plate  1). 

(See  "  A  Treatise  on  Masonry  Construction,"  by  I.  O.  Baker,  p.  286;  also 
Engineering  News,  vol  13,  p.  14;  and  "  A  Practical  Treatise  on  Foundations," 
by  W.  M.  Patton).  The  Havre  de  Grace  Bridge  is  single-track;  a  double- 
track  bridge  is  considered  in  the  present  text.  The  actual  caisson  is  of  wood; 
the  one  here  outlined  is  of  steel. 

-I.  The  writer  does  not  mean  to  imply  that  steel  is  better  than  wood  con- 
struction for  a  caisson  at  this  particular  pier  site.  He  has  arbitrarily  chosen 
steel  for  the  main  purpose  of  explaining  tersely  the  method  of  procedure.  The 
mechanical  principles  for  calculation  are  logically  outlined  and  the  main  parts 
of  the  caisson  are  designed  sufficiently  in  detail  to  satisfy  all  stress  conditions. 
In  short,  the  object  of  the  paper  is  to  emphasize  the  design  of  a  metal  caisson. 
It  may  be  further  observed  that  any  one  interested  may  have  the  opportunity 
of  comparing  the  results  of  the  present  problem  with  those  of  the  actual  con- 
struction. The  actual  caisson  being  of  wood  lends  itself  less  readily  to  compu- 
tation. 


78S4SO 


2  DESIGN    OF   A    RAILWAY    BRIDGE    PIER. 

5.  The  wood  caisson  now  in  the  work  at  pier  8  is  17  ft.  3  ins.  in  height,  and 
...   in  j»laiv  m.ea'stf.res  70  ft.  10J  ins.  x  32  ft.  7|  ins.     In  the  actual  bridge  a  520-ft. 
•••'  throtlgft  ^'pa^'and  a  380-ft.  deck  span  meet  at  the  pier.     In  the  present  problem 
.;  ^he^sscrne  deftgftis  of  span  are  assumed,  but  both  spans  are  treated  as  through 

•  '"types.'  •  Prg.*I,''Plate  1,  shows  a  profile  of  the  complete  bridge  and  the  position 
of  pier  8. 

II.   GENERAL  PROPORTIONS  OF  PROPOSED  PIER. 

6.  Plate  2  gives  the  main  dimensions  for  the  pier  outlined  in  the  present 
problem.     The  base  of  rail  is  at  an  elevation  of  +94.97  ft. ;   9  ft.  6  ins.  lower  is 
the  plane  of  the  coping  top.     The  coping  measures  27  ins.  in  thickness.      For  the 
next  79  ft.  downward,  horizontal  sections  of  the  pier  have  parallel  sides  and 
semicircular  ends  with  a  face  batter  of  £-in.  to  the  vertical  foot.     From  this 
elevation  the  cut-water  extends  on  the  up-stream  side  for  the  next  10  vertical 
ft.  with  a  slope  of  one  in  four,  while  the  other  sides  ret  ,in  their  normal  batters. 
The  cut-water  sections  end  24  ft.  above  the  mud-line.      From  the  base  of  the 
cut- water  to  the  mud -line  the  pier  section  remains  constant;  that  is,  the  pier 
sides  are  vertical.     At  the  mud-line  the  pier  enlarges  by  offsets  to  a  rectangular 
section  in  order  to  give  proper  anchorage  and  bottom  clearances  for  the  detach- 
able coffer-dam.     From  the  mud-line  downward,  with  batters  of  one  to  twenty- 
four  on  all  sides,  the  rectangular  section  continues  to  the  caisson  roof,  67  ft. 
below.     The  caisson  itself  has  vertical  sides,  and,  measured   along  its  outer 
side-plates,  is  12  ft.  2|  ins.  in  height.     From  the  cutting  edge  of  the  caisson  to 
the  top  of  the  coping,  the  pier  measures  179.94  ft.     Eighty-four  and  two-tenths 
feet  of  the  pier  are  below  the  low-water  line. 

7.  In  this  particular  problem  the  river  selected  has  but  a  small  range  in  water 
surface.     Bridge  piers  in  the  Mississippi  valley  rivers  require  the  consideration 
of  great  range  in  stage,  a  condition  which  often  produces  a  very  serious  problem. 
Eighty-six  and  twenty-four  hundred ths   (86.24)  feet  of  the  pier  is  above  low 
water.     From  low  water  to   the  river  bottom  measures  28.95  ft.     From  the 
river  bottom,  or  mud-line,  to  rock,  averages  55.05  ft.     At  low-water  stage  of 
the  river,  therefore,  the  greatest  head  on  the  caisson,  that  is,  when  it  has  reached 
its  destination,  is  about  55  ft.  of  material  (mud  and  silt)  and  29  ft.  of  water;   to 
be  exact,  84.2  ft.  in  all.     At  high  stage  of  the  river  2.75  ft.  of  water  must  be 
added  to  the  above  figures. 

8.  It  is  plain  that  the  foundation  is  a  rather  deep  one,  but  it  does  not  approach 
the  extreme  record  depths.     It  would  seem  that  pneumatic  work  reaches  the 
limit  of  its  application  for  depths  of  from  100  to  125  ft.  below  water  surface. 

III.     SPECIFICATIONS. 

9.  The  following  important  quantities  and  other  specifications  are  used  in 
the  calculations: 

a.  The  weight  of  pier  masonry  =  155  Ibs.  per  cu.  ft. 

b.  Weight  of  yellow  pine  timber  =  50  Ibs.  per  cu.  ft. 

c.  Weight  of  concrete  =  140  Ibs.  per  cu.  ft. 

d.  Weight  of  steel  and  iron  =  480  Ibs.  per  cu.  ft. 


DESIGN    OF   A    RAILWAY    BRIDGE    PIER.  3 

e    The  coping  course  is  of  granite. 

/.  From  the  coping  to  low  water  the  pier  consists  of  a  concrete  heart  [  1  Port- 
land cement,  3  sand,  5  broken  stone  (to  pass  a  2-in.  ring)]  faced  with  limestone 
ashlar  (quarry -faced,  joints  f-in.). 

g.  From  low  water  to  the  mud-line  of  river  bottom  the  whole  body  of  the 
pier  is  of  concrete  of  the  proportions  given  above. 

h.  From  the  mud-line  to  the  caisson  top  the  pier  consists  of  a  permanent 
coffer-dam  of  yellow  pine  filled  with  timber  framing,  but  mainly  with  concrete 
of  1  Portland  cement,  2  sand  and  4  broken  stone  (to  pass  a  2-in.  ring). 

i.  The  steel  caisson  is  eventually  filled  with  a  rich  concrete  composed  of  1 
Portland  cement,  2  sand  and  4  broken  stone  (to  pass  a  1-in.  ring). 

/.  The  total  weight  in  pounds  per  lineal  foot  for  the  main  trusses  and  their 
bracing  is  assumed  as  follows: 

For  the  380-ft.  span  =  10  times  the  span  length  in  feet,  =  3,800  Ibs. 

For  the  520-ft.  span  =  11.5  times  the  span  length  in  feet,  =  5,980  Ibs. 

These  weights  are  for  double-track  structures  and  are  somewhat  light,  con- 
sidering the  heavy  locomotives  now  being  proposed ;  for  example,  Cooper's  E-50. 
For  such  heavy  loadings  the  weights  of  trusses  of  the  above  spans  should  be 
increased  to  say  13  and  15  times  the  span  length  in  feet,  respectively. 

k.  Weight  of  floor  system  =  900  Ibs.  per  lineal  foot.  This  figure,  also,  is 
light. 

/.    Weight  of  track  =  800  Ibs.  per  lineal  foot. 

m.  Average  weight  of  live-load  =  3,500  Ibs.  per  lineal  foot. 

n.  Through  trusses  for  general  lateral  stability  should  have  a  spacing  equal 
to  or  greater  than  one-eighteenth  to  one-twentieth  of  the  span.  In  the  present 
case  the  spacing  has  been  assumed  28  ft.  6  ins.  This  would  seem  rather  re- 
stricted, considering  the  520-ft.  span,  but  it  is  justifiable,  since  most  of  the 
spans  of  the  Havre  de  Grace  bridge  are  shorter.  Heavy  train  loadings  like 
Cooper's  E-50,  for  proper  clearances,  would  find  this  spacing  of  trusses  rather 
scant.  Twenty-nine  feet  six  inches,  or  even  30  ft.  would  be  advisable  for  post 
clearances,  especially  the  end-posts. 

The  calculations  here  given  were  made  some  time  ago  for  the  28  ft.  6-in. 
spacing,  and  the  writer  has  not  had  the  time  at  his  disposal  to  make  a  desirable 
change.  This  is  true  of  other  parts  of  the  calculations.  The  article  attempts 
to  explain  a  method  rather  than  to  give  in  all  cases  the  most  stii  table  proportions. 

o.  The  allowable  pedestal  bed-plate  pressure  is  350  Ibs.  per  sq.  in. 

p.  Specifications  for  individual  materials,  for  timber  construction  and  stone 
masonry  are  not  given.  They  may  be  found  in  any  standard  set  of  specifications 
for  substructures.  Consult,  for  example,  "General  Specifications  for  Bridge 
Sub-Structure,"  of  the  Osborn  Company. 

IV.     NECK  SECTION  OF  PIER. 

(See  Plate  1,  Fig.  2.) 

10.  The  size  and  shape  of  the  neck  section  of  a  pier  depend  upon  the  bracing 
of  the  main  trusses  and  upon  the  bed-plate  dimensions  of  the  bridge  pedestals. 
The  truss  spacing  has  already  been  given  as  28  ft.  6  ins.  The  bed-plates  must 


DESIGN    OF    A    RAILWAY    BRIDGE    PIER. 


DESIGN    OF    A    RAILWAY    BRIDGE    PIER.  5 

now  be  designed.     The  total  weight  of  superstructure  and  train  possible  upon 
one  pedestal  is  as  follows: 

For  the  380-ft.  span  =  1,187,500  Ibs. 

For  the  520-ft.  span  =  1,908,400  Ibs. 

11.  These  loads  must  be  carried  by  the  respective  pedestal  bed-plates.     The 
working  values  for  allowable   bed-plate  pressure  on  granite  copings    vary  with 
different  designers  from  300  to  400  Ibs.  per  sq.  in.     An  average  value  of  350 
Ibs.  per  sq.  in.  is  here  taken  and  the  bed-plates,  therefore,  require  the  following 
areas : 

For  the  380-ft.  span  -  24  1  sq.  ft. ;  final  7  ft.  x  3  ft.  6  ins. 
For  the  520-ft.  span  =  38.7  sq.  ft. ;  final  7  ft.  x  5  ft.  6  ins. 

12.  It  is  plain  that  the  area  of  pier  top  or  neck  section  must  be  far  greater 
than  is  necessary  for  the  masonry  to  carry  the  loads.     The  pedestal  plates  are 
made  oblong  to  save  width  of  pier,  since  its  length  is  fixed  by  the  truss  spacing. 
Where  trusses  require  a  very  wide  spacing,  piers  sometimes  omit  a  portion  of 
the  central  masonry.     In  such  cases  we  virtually  have  two  visible  piers,  one 
under  each  set  of  bridge  pedestals,  resting  upon  a  common  foundation.     In  a 
construction  of  great  magnitude  not  only  the  visible  piers  but  the  foundation 
also  may  become  entirely  separated  from  the  two  sides  of   the  structure,  pro- 
ducing two  independent  piers  and  foundations.     Much  economy  may  often  be 
possible  through  a  careful  study  of  this  problem. 

13.  It  will  be  noticed  that  the  bed-plates  for  both  spans  are  slightly  wider  than 
necessary,   assuming  the  7-ft   sides  as    fixed  lengths.      This   increase    allows 
for  expansion  and  contraction  of  the  trusses,  due  to  changes  of  temperature. 
Good  practice  allows  one  inch  per  100  feet  of  span  for  the  total  expansion  from 
a  mean  position,  and  the  same  amount  for  contraction,  as  a  horizontal  play-room 
for  the  roller -ends  of  the  trusses.     Eight  inches  is  allowed  for  the  480-ft.  span; 
the  above  rule  requires  7. 6 ins.     A  proportional  allowance  has  been  made  for 
the  520-ft.  span,  assuming  that  both  trusses  meet  at  pier  8  with  expansion 
bearings.     This    may  or  may  not  be  the  case.     If   desired,  therefore,  a  few 
inches  could  be  saved  in  the  width  of  pier  by  treating  one  or  both  pedestals 
as  fixed.     The  width  of  the  neck  section  finally  adopted  is  10  ft.  6  ins  ,    the 
total  width  of  bed-plates  with  expansion  allowance  is  9  ft.  8  ins.     It  is  desirable 
always  to  have  the  neck-section  width  slightly  exceed  the  bed-plate  plans. 

14.  This  pier  has  semicircular  ends.     The  diameter  of  the  semicircle  for  the 
neck  section  is  taken  along  the  extreme  outer  edges  of  the  bed-plates.     Fig.  2, 
Plate  1,  gives  the  final  proportions  for  the  pier  top.     Fig.  3  shows  a  study  for 
the  coping  and  corbel  courses.     Copings  should  ordinarily  project  about  6  ins. 
beyond  the  next  course  below  and  not  more  than  9  ins.     This  being  a  large  pier, 
the  upper  limit  is  taken.     In  deciding  upon  the  amount  of  projection,  the  gen- 
eral architectural  effect  should  be  considered.     The  corbel  course  is  added  for 
this  latter  purpose;  it  reduces  projections  per  course  at  the  same  time  that  it 
provides,  sufficiently  large  total  projection  for  heavy  piers.     The  introduction 
of  the  corbel  course  causes  the  smallest  section  of  the  pier,  which  is  at  the  base 
of  the  corbel  course,  to  be  slightly  larger  than  the  neck  section. 


6  DESIGN    OF    A    RAILWAY    BRIDGE    PIER. 

V.     GENERAL  STABILITY  OF  PIER. 

15.  A  high  pier  is  subject  to  the  vertical  loads  of  the  superstructure  and  its 
own  weight,  and  its  horizontal  section  at  any  level  must  be  of  sufficient  area  to 
withstand  the  vertical  load  at  proper  working  pressure. 

16.  At  the  foundation  beds  these  loads  must  be  carried  with  proper  working 
factors,  depending  upon  whether  the  caisson  material,  or  the  material  upon 
which  it  rests,  is  the  weaker,  in  supporting  power.     For  example,  a  pier  resting 
on  sound,  solid  rock,  will  carry  loads  dependent  upon  the  crushing  strength  of 
the  caisson  materials,  but  if  the  same  pier  rested  on  sand  the  crushing  strength 
of  the  pier  concrete  would  exceed  the  safe  supporting  power  of  the  sand.     Other 
things  being  equal,  the  bottom  plan  of  a  pier  would  have  to  be  much  larger  for 
a  sand  than  for  a  rock  foundation. 

17.  In  these  calculations  must  be  considered  the  abnormal  pressure  on  the 
foundation  bed,  the  buoyant  efforts  of  the  displaced  water  and  the  friction  and 
uplifting  forces  exerted  by  the  surrounding  material  against  the  sides  of  the  pier 
and  foundation. 

18.  The    vertical   loads    produce  compression,   usually    of  nearly    constant 
intensity  upon  horizontal  sections  of  the  foundation.     This  condition  of  loading 
is  practically  obtained  for  a  pier  of  equal  batter  on  all  sides.     Our  pier  has  a 
starling  on  the  up-stream  face  which,  for  sections  below  it,  throws  the  resultant 
weight  away  from  the  center  of  horizontal  sections  and  toward  the  down-stream 
edge;  therefore  the  dead  weight  of  the  superstructure  and  pier  tends  to  produce 
pressures  slightly  greater  at  the  down-stream  toe  than  at  the  up-stream.     In 
most  piers,  as  in  this  example,  the  variation  is  slight  and  commonly  neglected. 

19.  There  are  other  reasons,  however,  why  the  pressures  at  times  may  vary 
greatly  in  intensity  upon  horizontal  sections  of  the  foundation,  especially  those 
at  considerable  depths.     Horizontal  forces  may  act  tending  to  overturn  the 
pier  about  its  down-stream  toe  and  in  a  plane  at  right  angles  to  the  length  of 
the  bridge.     Fig.  4,  Plate  1,  shows  the  nature  and  position  of  these  forces.     They 
are  produced  by  the  wind  on  the  trusses  and  train,  the  wind  on  the  pier,  the 
pressure  of  an  ice-flow  through  which  the  pier  cuts,  and  the  pressure  of  the 
water  current  moving  against  the  structure.     These  forces  may  all  act  in  the 
same  direction  and  at  the  same  time.     Their  overturning  moment  tends  to 
produce  compression  on  the  down-stream  half  of  a  horizontal  section  and  tension 
on  the  up-stream  half.     Under  the  most  favorable  action  of  these  horizontal 
forces,  therefore,  we  may  find  a  much  higher  intensity  of  pressure  at  the  down- 
stream than  at  the  up-stream  edge  of  a  joint. 

20.  To  study   these  stresses  it  is  necessary   to  consider  for  any   horizontal 
joint  the  stability  of  the  structure  against: 

a.  Pressures  due  to  vertical  loads. 

b.  Overturning  about  the  down-stream  toe. 

c.  Horizontal  sliding  down-stream. 

d.  Maximum  intensity  of  pressure  at  down-stream  toe. 

21.  Calculations  of  this  type  present  no  difficult  problem  and  are  well  outlined 
in  such  books  as  Baker's  "  Masonry  Construction,"  Chapter   16,  p.   366.     In 
order  to  design  the  steel  caisson  in  this  problem,  however,  it  is  necessary,  first. 


DESIGN    OF   A    RAILWAY    BRIDGE    PIER.  7 

to  make  sure  that  the  pier  is  stable  and  economic,  and  consequently  the  sta- 
bilities of  joints  MN,  G  H  and  JK  (see  Plate  2),  are  considered.  These 
joints,  it  will  be  noted,  are  at  the  mud-line,  caisson  roof  and  rock  bottom  re- 
spectively. Joints  above  the  mud-line  need  not  be  considered,  because  the 
loads  and  overturning  effects  are  relatively  small. 

VI.     HORIZONTAL  FORCES  ACTING  UPON  PIER  AND  SUPERSTRUCTURE. 

(See  Plate  1,  Fig.  4.) 

22.  F ,  =  wind  pressure  on  520-ft.  trusses  =  78,000  Ibs.  acting  at  elevation 
+  120.03. 

F2  =  wind    pressure   on    380-ft.    trusses  =  57,000    Ibs.    acting    at    elevation 
+  115.03. 

F3  =  wind  pressure  on  train  =  135,000  Ibs.  acting  at  elevation   +   105.03. 
F t  =  wind  pressure  on  pier  =  23,240  Ibs.  acting  at  elevation   +  45.28. 
F5  ±=  ice  thrust  =  743,040  Ibs.  acting  at  elevation   +   0.28. 
Ft  =  current  pressure  =  13,500  Ibs.  acting  at  elevation  —  9.72. 
Total  horizontal  force  tending  to  produce  sliding  =  1,049,780  Ibs. 

23.  In  the  above:      (1)  The  vertical  projection  of  trusses  has  been  assumed 
equal  to  10  sq.  ft.  per  lineal  foot  of  span  and  that    of  trains  at  the  same  figure; 
(2)  the  wind  pressure  on  vertical  projections  of  trusses  and  train  is  assumed  at 
30  Ibs.  per  sq.  ft.  and  on  the  pier  at  20  Ibs.  per  sq.  ft.,  because  the  ends  are  round 
and  tend  to  deflect  the  wind;   (3)  the  ice- flow  is  assumed  to  be  1.5  ft.  thick  of 
melting  ice  with  a  crushing  strength  of  200  Ibs.   per  sq.   in. ;  (4)  the  current 
pressure  is  computed  by  formula,  Art.  569,  p.  367,   of  Baker's  "  Masonry  Con- 
struction." 

24.  In  determining  the  elevations  for  the  horizontal  forces,  the  520-ft.  truss 
is  assumed  60  ft.  in  depth  and  the  380-ft.  truss  at  50  ft. ;  the  lower  chord  of  both 
trusses  is  taken  5  ft.  below  thebaseof  rail,  the  train  wind  10ft.  above  base  of  rail; 
the  ice-flow  is  considered  to  occur  at  high-water,   and    the    resultant    current 
pressure  is  placed  20  ft.  above  the  river  bottom  for  a  river  depth  at  high-water 
of  about  32  ft. 

These  figures  are  not  exact,  but  greater  accuracy  is  not  necessary. 

VII.     STABILITY  OF  SECTION  MN. 

25.  Elevation  =  — •  29.72  at  the  mud-line  or  river  bottom. 

Weight  of  the  pier  above  MN  =  13,119,820  Ibs.  L,  _, 

Weight  of  live  load  and  superstructure  =  6,191,800  Ibs. 

Total  weight  on  section  MN  =  19,311,620  Ibs. 

Total  weight  (deducting  for  empty  cars)   ==  18,186,620  Ibs. 

Area  of  section  MN  =  964.9  sq.  ft. 

Total  horizontal  force  above  MN  =  1,049,780  Ibs. 

26.  Stability  Against  Overturning,  Section  M  N.     Using  similar  notation   to 
that  for  the  horizontal  forces,  the  moments  of  these  forces  about  axes  in  the 
section  MN  are  as  follows: 

M,  =     78,000  x  150  =  11,700,000  ft.-lbs. 
M2  =    57,000  X  145  =    8,265,000  ft.-lbs. 


8  .DESIGN    OF    A    RAILWAY    BRIDGE    PIER. 

M,  =  135,000  X  135  =  18,225,000  ft.-lbs. 
M4  =  23,240  X  75  =  1,743,000  ft.-lbs. 
Ms  =  743,040  X  30  =  22,291,200  ft.-lbs 
Mt  =  13,500  x  20  =  270,000  ft.-lbs. 
Total  overturning  moment  for  section  MN  =  62,494,000  ft.-lbs. 

27.  The  lever-arm,  with  respect  to  MN  of  the  resultant  of   all  the  horizontal 
forces    acting   upon    the    structure  =  62,494,000  +•  1,049,780  =  59.5    ft.     The 
resultant  of  this  maximum  horizontal  overturning  force  and  the  vertical  load 
above  MN  cuts  that  joint  at  the  point  E,  Plate  2,  far  within  the  middle   third. 
There  can  never  be  tension  in  the  section,  and  there  is  no  danger  from  over- 
turning. 

28.  Stability  Against  Sliding,  Section  M  N.     The  resultant   at  E  makes    an 
angle  with  the  vertical  whose  tangent  =  1,049,780  +  18  186,620  =  0.058. 

At  the  limit  for  sliding  stability  the  value  of  this  tangent  for  masonry  is 
0.75,  which  shows  that  the  joint  has  a  frictional  resistance  to  sliding  thirteen 
times  greater  than  is  necessary  just  to  balance  the  horizontal  forces.  Besides 
the  frictional  resistance  the  joint  offers  also  a  shearing  resistance,  usually  neg- 
lected in  calculations  of  this  kind,  though  it  is  a  very  large  quantity.  These 
results  emphatically  show  that  sections  like  MN  are  abundantly  able  to  resist 
sliding. 

29.  Safety  Against  Crushing,  Section  M  N.     The  vertical  loads  acting  alone, 
assuming  a  uniform  distribution   of  pressure,   produce  a   compression  in   the 
joint  MN  of  an  amount: 

p  =  19,311,620  •*-  964.9  =  19,900  Ibs  per  sq.  ft.  =  10  tons  per  sq.  ft.  Good 
concrete  may  safely  carry  15  tons  per  square  foot.  The  value  of  p  is  not  exact 
because  the  load  is  probably  not  uniformly  distributed  and  because  the  resultant 
load  does  not  cut  the  center  of  the  joint,  but  passes  slightly  to  the  down-stream 
side  of  the  center  a  distance,  e.  This  eccentricity  is  due  to  the  cut-water. 

30.  A  moment  Pe  therefore  tends  to  produce  tension  in  the  up-stream  half 
and  compression  in  the  down-stream  half  of  the  joint.     P  is  the  total  load  on 
the  joint;  the  maximum  intensity  of  pressure  occurs,  consequently,  at  the  down- 
stream edge.     Its  amount  is 


where  /  is  the  longer  side  of  the  joint,  and  /  the  moment  of  inertia  of  the  joint 
about  its  shorter  center  line.  In  the  present  case  e  is  small  and  the  value  of  pt 
is  assumed  essentially  equal  to  p. 

31.  It  has  already  been  shown  that  the  horizontal  forces  produce  an  over- 
turning moment,  M  =  62,494,000  ft.-lbs.  (Art.  26).  This  moment  produces  a 
similar  effect  to  that  discussed  for  the  moment  Pe,  but  it  cannot  be  neglected. 
In  general, 

' 


Neglecting  Pe,  the  greatest  compressive  intensity  for  the  joint  M  N  is 
pt  =  19,900  +  6,900  =  26,800  Ibs.  per  sq.  ft.   =  12.4  tons  per  sq.  ft. 


DESIGN    OF    A    RAILWAY    BRIDGE    PIER.  9 

Again  these  calculations  are  not  exact,  but  were  roughly  made  to  save  time 
and  labor.  The  relatively  high  values  for  the  pressures  indicate  an  economic 
design. 

32.  The  calculations  in  Arts.  25  to  31  show  that  the  section  MAT,  at  the  mud- 
line,  is  perfectly  stable  in  all  respects. 

VIII.     STABILITY  OF  CAISSON-ROOF  SECTION. 

33.  This  section  GH,  see  Plate  2,  is  43  ft.  below  section  MTV.      The    total 
weight  upon  GH  is  28,600,000  Ibs.     The  area  of  section  GH  =  68X27  =  1,836 
sq.  ft.,  therefore  the  average  pressure,  p  =  15,600  Ibs.  per  sq.  ft.  =.7.8  tons 
per  sq.  ft.     The  total  horizontal  force  is  the  same  as  for  MTV;    the  factor  of 
safety  against  sliding   (neglecting  shearing  tenacity)   is  about    18.     Since  the 
joint  is  43  ft.  below  MTV,  the  total  overturning   moment  is  readily  obtained  as 
follows:  M  =  62,494,000+  (1,049,780X43)  =  107,700,000  ft.-lbs.     Substituting  in 
Equation  (2),  again  neglecting  the  small  amount  Pe,  the  maximum    pressure 
at  the  down-stream  edge  is  p2  =  15,600  +  5,130  =  20,730  Ibs.  per  sq.  ft.  =  10.3 
tons  per  sq.  ft.     The  most  eccentric  position  of  the  resultant  cuts  the  joint  at 
F  (see  Plate  2),  far  within  the  middle  third. 

IX.     STABILITY  OF  PIER  AT  BED  ROCK. 

34.  The  total  weight  of  superstructure  and  pier  resting   upon  bed-rock  is 
33,000,000  Ibs.     The  caisson  plan  is  68X27  =  1,836  sq.  ft.     The  average  in- 
tensity of  pressure  due  to  weight  alone  =  17,900  Ibs.  per  sq.  ft.  =  9  tons  per 
sq.  ft.     In  the  two  previous  joints  the  strength  against  sliding  was  shown  to  be 
great;  as  it  must  be  even  greater  in  this  case,  the  computations  are  omitted. 
Bed-rock  is  55.2  ft.  below  section  MTV,  hence  the  total  overturning  moment    is 

M  =  62,494,000 +(1,049,780X55.2)   ==  120,694,000,ft.-lbs.,  and  p2  =  17,900  + 
5,700  =  23,600  Ibs.  per  sq.  ft.  =  12  tons  per  sq.  ft. 

35.  The.se  pressures  are  safe  for  concrete  and  bed-rock,   but  would  be  too 
high  for  a  foundation  on  sand.     If  this  pier  rested  on  sand,  it  would  require 
a  much  larger  caisson  plan  to  reduce  the  loads  on  the  sand.       A  steel  caisson 
would  be  out  of  place  in  such  a  case.     Wood  beirg  lighter  and  of  larger  volume 
would  be  far  more  suitable  material.     The  pier  at  bed-rock  is  very  safe  against 
overturning;  the  resultant  load  may  be  shown  to  pass  far  within  the  middle 
third  of  the  section. 

36.  The  stiffness  of  the  surrounding  material  must  assist  the  structure  against 
sliding  and  overturning  for  joints  below  the  mud-line,  but  such  resistance   cannot 
be  considered,  since  the  pier  must    never   appreciably    move.      Nevertheless, 
piers  deeply  imbedded  in  materials  like  mud,  silt,  sand,  clay  and  hardpan,  and  es- 
pecially the  last  three  materials,  must  be  made  additionally  stable  against 
overturning. 

37.  The  pressures  computed  above  for  bed-rock  perhaps  never  exist  and  are 
in  excess.     They  neglect  buoyancy  of  water  and  displaced  materials  and  omit 
the  supporting  effect  by  side  friction  from  the  surrounding  material.     If  no 
water  can  get  under  the  pier,  a  condition  rarely  obtained,  buoyancy  will  not 
enter  to  reduce  the  pressures  on  bed-rock.     The  following  figures  are  significant: 


10 


DESIGN    OF    A    RAILWAY    BRIDGE    PIER. 


PLATE  2. 


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GZWZftAZ.  7ZAN 


DESIGN    OF   A    RAILWAY    BRIDGE    PIER.  II 

Total  load  of  structure  on  bed-rock  =  33,000,000  Ibs. 

Buoyancy  of  displaced  water  =  1,750,000  Ibs. 

Immersed  weight  =  31,250,000  Ibs. 

Buoyancy  of  sand  and  silt  at  120  Ibs.  per  cu.  ft.   =  77,325,000  Ibs. 

Fatigue  weight  =  19,925,000  Ibs. 

Side  friction  at  400  Ibs.  per  sq.  ft.  of  surface  =  4,075,000  Ibs. 

Actual  probable  fatigue  measure  =  15,850,000  Ibs. 

=  8,600  Ibs.  per  sq.  ft. 

=  4.3  tons  per  sq.  ft. 

X.     BATTERS  AND  THEIR  EFFECT  ON  THE  STABILITY  OF  PIERS. 

38.  The  computations  for  the  three  joints  here  studied  show  that  it  is  unnecessary 
to  consider  the  stability  of  sections  above   the  mud-line.      Such   sections  will 
be  more  than  strong  enough,  especially  near  the  pier  top.     In  fact    it   may  be 
said  that  very  deep  piers,  piers  that  have  sufficient  neck  section  to  carry   the 
superstructure,  which  have  side  batters  of  1  in  12  to  1  in  24,  will  be  found  stable 
in  most  cases.     Exceptions  to  this  rule  will  be  found  for   very   deep   and  high 
piers  resting  upon  poor  foundation  material.     Such  cases  would   require   large 
bottom  plans  and  therefore  large  caissons,  and  such  caissons  had  better  be  of 
wood  than  of  steel.     Low  piers  requiring  large  neck  sections  will   generally   be 
of  excessive  strength. 

39.  In  this  case  the  batters,  for  simplicity  of  calculation,  have  been  taken  at 
J-in.  per  vertical  ft.  on  all  sides.     End  batters  are  often  made  larger  than  the 
side  batters,  being  perhaps  f-in.  per  vertical  ft.  as  against  f-in.  per  vertical  ft. 
for  side  batters.     Batters  are  indispensable  for  appearance,  but  where  stability 
does  not  warrant  a  batter,  there  is  no  reason  why  piers  may  not  have  vertical 
sides  below  permanent  low  water. 

XI.     FLOTATION  OF  CAISSON. 

40.  The  caisson  is  to  be  built  on  scows  which  are  to  be  weighted  and  sunk 
when  launching  time  comes.     Care  must    therefore  be  taken  to  design    the 
caisson  to  float,  cutting-edge  downward,  in  order  that  it  may  be  towed  to  the 
pier  site,  accurately  located,  and  held  in  position  by  cables  and  piles  preparatory 
to  the  work  of  sinking. 

41.  The  metal  weight  of  steel  caissons  is  found  by  experience  to  equal  usually 
from  11  to  13  Ibs.  per  cu.  ft.  of  enclosed  volume.     Using  the  average  figure  of 
12  Ibs.,  the  approximate  caisson  weight  is  68X27X12X12.2  =269,000  Ibs. 
Assuming  a  thickness  of  4  ft.  of  concrete  over  the  roof-plate  of  the  caisson's 
working  chamber  and  between  and  above  the  roof  girders  to  give  stiffness  and 
flotation  stability,  gives  a  weight  of  concrete  of  68X27X4X 155  =  1,138.320  Ibs. 
The  total  weight  of  steel  and  concrete  to  be  floated,  therefore,  is  about  1,400,000 
Ibs.,  requiring  a  displacement  of  22,400  cu.  ft.     Neglecting  the  volume  of  the 
working  chamber,  which  may  be  assumed  filled  with  water,  the  volume  of  water 
displaced  between  the  roof  level  and  the  top  of  the  caisson  side-plate  is  27  X 
68X4.8  =  about  8,810  cu.  ft.,  leaving  13,590  cu.  ft.,    of   displacement  to  be 
produced  by  adding  to  the  caisson  top  a  sufficient    height  of  timber  wall  of  the 


12  'DESIGN    OF   A    RAILWAY    BRIDGE    PIER. 

permanent  coffer-dam.     A  height  of  7.4  ft.  of  such  timber  wall  is  therefore 
necessary  to  secure  flotation  with  a  4-ft.  layer  of  concrete. 

42.  It  is  highly  improbable  that  the  caisson  will  be  loaded  with  a  weight 
equivalent  to  a  4-ft.  thickness  of  concrete,  but  for  flotation  safety  it  would  seem 
advisable  that  at  least  7  ft.  of  permanent  coffer-dun  wall  should  be  in  place 
and  calked  when  the  caisson  is  launched  and  towed  to  the  pier  site. 

XII.     WEIGHT  NECESSARY  TO  SINK  CAISSON. 

43.  After  the  caisson  is  moored  in  position  at  the  pier  site  it  becomes  necessary 
in  order  gradually  to  sink  the  structure,  to  weight  it  by  increasing  amounts,  at 
the  same  time  adding  to  the  height  of  the  permanent  coffer-dam  wall  to  keep 
water   from    entering   the   pier   volume   from   above.     Until   the   cutting-edge 
reaches  the  river  bottom  or  mud-line,  the  only  weight  necessary  for  sinking  is 
that  required  to  overcome  water  buoyancy.     Such  sinking  weight    is    readily 
obtained  by  adding  in  layers  the  concrete  of  the  permanent  coffer-dam.     But 
when  the  caisson  has  once  reached  the  river  bottom,  the  sinking  weight  necessary 
must  not  only  overcome  water  buoyancy,  but  also  side  friction  and  resistances 
at  the  cutting-edge  offered  by  the  materials  through  which  the  caisson  is  being 
sunk.     As  the  structure  proceeds  downward  from  the  river  bottom  to  bed-rock, 
the  frictional   resistance  rapidly   increases  in  amount,   so   that   the  necessary 
sinking  weight  becomes  rapidly  larger,  reaching  its  maximum  during  the  last 
operation  of  sinking,  when  the  caisson  is  just  about  to  reach  its  final  position. 

44.  The  exact  value  of  this  sinking  weight  cannot  be  accurately  computed 
because  the  conditions  which  determine  the  uplifting  and  resisting  forces  are  too 
complex  and  uncertain  to  allow  of  close  calculation.     The  designing   engineer 
must  therefore  provide  a  caisson  strong  enough  to  carry  a  load  safely  in  excess 
of  the  probable  maximum  sinking  weight.     When  the  pier  has  once  reached 
bed-rock  no  further  weight  is  added  to  the  structure  until  the  caisson   volume ' 
has  been  filled  with  concrete  and  the  air-locks  and  as  much  as  possible  of  the 
air-shafts  for  men  and  material  have  been  removed.       It  is  plain,  therefore, 
that  the  caisson  stresses  are  not  due  to  the  final  pier  weights. 

45.  The  stresses  acting  in  the  caisson  frame  are  temporary  and  cease  to  exist 
after  the  caisson  has  been  firmly  seated  on  bed-rock  and  its  working  chamber 
filled  with  concrete.     High  working  stresses,  at  least  one-half  the  elastic  limit 
of  the  metal,  are  consequently  justifiable.     This  explains  the  relatively  high 
values  in  the  following  design  calculations:  20,000,  Ibs.  per  sq.  in.  is  used  for 
direct  stresses  and  10,000  Ibs,  per  sq.  in.  for  shearing  stresses. 

46.  Sometimes  the  maximum  necessary  sinking  weight  is  not  all    produced 
by  materials  of  the  actual  final  pier.     Loads  of  pig-iron  are  often  used  rather 
than  the  weight  of  materials  of  the  completed  structure.     The  pig-iron  acts  as  a 
live-load,  so  to  speak,  and  may  be  varied,  increased,  and  also  decreased,  if  found 
desirable.     The  engineer  thereby  obtains  a  greater  command  over  the  sinking 
operations,  especially  when  the  foundation  tends  to  careen  or  turn  from  its 
proper  alinement. 

47.  Side  frictional   resistances   offered  by   materials  like  those  encountered 
at  Havre  de  Grace  will  usually  be  found  between  350  and  450  Ibs.  per  sq.  ft. 


DESIGN    OF    A    RAILWAY    BRIDGE    PIER. 


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DESIGN    OF    A    RAILWAY    BRIDGE    PIER. 


;     _         _  DESIGN   OF   A    RAILWAY    BRIDGE    PIER.  15 

of  surface,  although  there  are  cases  on  record  where  frictional  resistances  of 
600  Ibs.  and  over  have  been  recorded.  The  maximum  area  over  which  the  fric- 
tional forces  act  is  10,192  sq.  ft.  Assuming  a  frictional  intensity  of  400  Ibs.  per 
sq.  ft.,  the  maximum  frictional  resistance  equals  about  10,492  x400  =  4,076,800 
Ibs.  The  volume  of  pier  under  water  is  114,312  cu.  ft.,  causing  a  buoyant 
force  due  to  displaced  water  of  about  7,154,500  Ibs.  The  greatest  resultant 
frictional  and  buoyant  force  is  therefore  in  the  neighborhood  of  11,231,300  Ibs. 
To  this  amount  should  be  added  resisting  forces  at  the  cutting-edge. 

48.  The  approximate  weight  of  steel  in  the  caisson  has  already  been  stated 
as  269,000  Ibs.,  Art.  41,  and  the  weight  of  pier  materials  between  the  caisson 
roof  and  the  water-line  is  about   14,303,400  Ibs.,  so  that  were  the  pier  to  be 
built  to  the  level  of  the  river  surface  at  the  time  the  cutting-edge  reached  bed- 
rock,  the  weight  of  pier  available  to  cause  sinking  would  be  approximately 
14,500,000  Ibs.     The  above  figures  show  that  such  a  weight  would  only  slightly 
exceed  the  probable  maximum  resistance  to  sinkage.     This  design,  therefore, 
assumes  that  under  the  worst  conditions  the  steel  caisson  must  be  able  to  support 
a  load  of  14,500,000  Ibs.,  and  that  at  the  same  time  it  must  be  capable  of  with- 
standing the  maximum  lateral  pressures  from  the  surrounding  material  tending 
to  thrust  inward  the  side  walls  of  the  working  chamber. 

XIII.     DESIGN  OF  CAISSON. 

49.  The  important  parts  of  the  steel  framing  of  the  caisson  are:  (1)  the  roof- 
plates,  (2)  roof-beams,  (3)  side-plates,  (4)  side-wall  brackets,  (5)  side-wall  beams, 
(6)  cutting-edge  and  (7)  splice-plates,  corner-plates  and  other  important  details. 

50.  Roof-Plates — The  roof-plates  carry  no  important  stresses;  they  are  f-in. 
thick  and,  like  the  side-plates,  must  be  carefully  calked  at  all  joints  to  secure 
as  nearly  as  feasible  a  water-tight  air-chamber. 

51.  Roof-Girders — The    roof -beams    are    plate-girders    spanning    the    shorter 
side  of  the  caisson  plan  and  are  supported  by   the  side-wall  brackets.     The 
masonry    above   them    has    considerable    supporting   power    itself.     The    steel 
girders  are  designed  to  carry  only  the  weight  of  a  wedge  of  material  whose  base 
is  the  caisson  roof  and  whose  sides  make  angles  of  thirty  degrees  with  the  vertical. 
See  Fig.  5,  Plate  1.     The  height  of  wedge  h  =  12  tan  60°  =  20.8  ft.     Due  to 
to  the  carrying  capacity  of  the  side- wall  brackets,  the  effective  span  of  the  girders 
is  taken  at  24  ft. ;  the  wedge  base  is  therefore  also  24  ft.     The  weight  of  1  ft. 
thickness  of  wedge  =  12X20.8X  155  =  38,700  Ibs. 

52.  Design  of  Flanges;  Roof -Girders — With  roof-beams  spaced  4  ft.  center  to 
center,  the  effective  reaction  for  one  girder  =  R  =  38,700x2  =  77,400  Ibs., 
while  the  maximum  bending  moment  in  the  span  equals  77.400X8=619,200 
ft.-lbs  ,  nearly.     For  a  beam-depth  of  £  the  span  the  plate-girder  web  is  36  ins. 
in  depth.     Assuming  flange-angles  6x4  ins.,  with  the  6-in.  leg  horizontal,  gives 
an  effective  depth  of  girder  =  34  ins.     If  the  flange-angles  be  considered  to 
carry  all  the  bending,  the  maximum  flange-stress  for  a  34-in.  effective  depth 

=  219,000  Ibs.  For  a  working  intensity  of  flange-stress  of  20,000  Ibs.  the 
flange-area  required  at  the  center  of  the  tension  flange  =  10.95sq.  ins.  Two6x4x 
j-in.  angles,  deducting  for  two  rivet-holes,  give  a  net  area  of  about  12.4  sq.  ins. 


16  DESIGN   OF   A    RAILWAY    BRIDGE    PIER. 

53.  Design  of  Web;  Roof-Girders — The  maximum  end  shear  of  77,400  Ibs., 
at  a  working-stress  intensity  of  10,000  Ibs.,  requires  7.74  sq.  ins.  of  available  web- 
section.     Assuming  J-in.  rivets  with  3-in.  pitch  in  the  stiffener-angles  gives  an 
effective  web-depth  of  24  ins.,  and  therefore  a  necessary  web-thickness  of  0.322 
in.     A  f-in.  web-plate  is  used.     Stiffener-angles  and  rivet  details  are  shown  on 
Plate  3.     Since  these  girders  are  imbedded  in  concrete,  their  webs  and  com- 
pression  flanges  are  considerably   reinforced.     The  stiffener-angles  are  conse- 
quently light,  being  two  3  X  3  X  $  in.  angles  occurring  about  every  3  ft.     Strictly 
speaking,  there  are  no  end  stiffeners.     Three  sets  of  stiffener-angles  are  found 
over  the  brackets.     The  stiffeners  at  the  extreme  ends  of  the  girders  are  made 
heavy,  of  two  6  X  6  X  J-in.  angles,  to  give  solid  connections  to  the  side-plates  and 
for  vertical  reinforcement  to  assist  in  carrying  the  extra  loads  which  come  upon 
the  brackets. 

54.  The    drawings    show    no    transverse    bracing   between    girders.     This   is 
deemed  unnecessary   because   of   the  binding  strength  of   the   concrete.     For 
security,  however,  two  lines  of  bracing  could  readily  be  introduced  along  lines 
AB  and  CD,  see  Plate  6. 

55.  Side-Plates — The  side-plates  are   f-in.    in   thickness.     As   they   are  rein- 
forced every  4  ft.,  horizontally,  by  the  main  side-wall  brackets,  and,  vertically, 
every  27  ins.  by  the  Z-bars,  they  must  simply  be  of  sufficient  strength  to  resist 
the  pressures  of  material  from  without  tending  to  bulge 27  X  48-in.  plates  inward. 
The  maximum  head  on  the  caisson  is  about  82  ft.,    of  which  about  30  ft.  is 
water,  and  the  rest  water  and  material.     Assuming  a  blow-out  to  occur  in  the 
working  chamber  and  that  the  82  ft.  head  of  water,  mud,  sand  and  silt  causes 
a  hydrostatic  pressure  equivalent  to  a  material  of  four-thirds  the  density  of 
water,  the  normal  intensity  of  bulging  pressure  has  a  maximum  value  of  about 
0.434X82X1.33X144  =  6,830  Ibs.  per  sq.  ft.   =  47.5  Ibs.  per  sq.  in. 

56.  The  intensity  of  pressure  is  roughly  obtained  and  may  be  very  excessive. 
Yet  it  would  be  unsafe  to  consider  a  smaller  pressure,  as  the  following  additional 
calculation  shows:  30  ft.  of  water  at  62  5  Ibs.  per  cu.  ft.  +  52  ft.  of  material  at 
120  Ibs.  per  cu.  ft.  produce  a  vertical  intensity  of  pressure  at  bed-rock  =  (30  X 
62.5)  + (52X120)   =8,100  Ibs.  per  sq.   ft.,   nearly.     The    horizontal  conjugate 
pressure,  according  to  Rankine,  is 

.   1  —  sin<£ 

p=wh-— — — £;  (3) 

1  +  sm  <f> 

where  wh  =  8,100  Ibs.  per  sq.  ft.  in  this  case  and  </>  the  angle  of  repose  of  the 
material  surrounding  the  caisson.  The  value  of  <£  must  lie  between  zero  and 
about  30°,  approaching  the  former,  the  wetter  the  material. 

For  0  =    0°,  p  =  8,100  Ibs.  per  sq.  ft. 

For  0  =  15°,  p  =.  8,100X0.588  =  4,780  Ibs.  per  sq.  ft. 

For  <j>  =  30°,  p  =  8,100X0.333  =  2,710  Ibs.  per  sq.  ft. 

Any  considerable  percentage  of  water  permeating  the  material  around  the  work- 
ing chamber  when  near  bed-rock  must  tend  to  cause  the  lateral  pressure  to 
approach'  8,100  Ibs.  per  sq.  ft. 

57.  The  unsupported  dimensions  of  plate  are  27  X  48  ins.,  Art,  55,     These 


DESIGN    OF    A    RAILWAY    BRIDGE    PIER. 


17 


18  DESIGN    OF   A    RAILWAY    BRIDGE    PIER. 

edges  cannot  be  said  to  be  simply  supported,  nor  can  they  be  assumed  entirely 
fixed.  The  theory  of  stress  in  bulged  plates  is  a  very  complex  subject.  Consult 
Burr's  "  Elasticity  and  Resistance  of  the  Materials  of  Engineering",  Art.  105,  p. 
184,  Edition  of  1903.  For  Burr's  notation,  a  =  27  ins.,  b  =  48  ins.,  w  =  47.5- 
Ibs.  per  sq.  in.  Assuming  fixed  edges,  the  greatest  intensity  of  fiber  stress  is 

a2  b4  w  . 

1  ~      *     <      4' 


and  t-t.VfflV-jp,  (5> 

Here  t  is  the  necessary  plate-thickness  in  inches,  and  .K",  the  allowable  intensity 
of  stress  in  Ibs.  per  sq.  in. 

58.  If  Kl  be  taken  at  20,000  Ibs.  per  sq.  in.,  t  =  0.952  ins.     The  above  calcu- 
lations are  only  roughly  approximate.     A  formula  expressing  the  thickness  t 
should  be  based  in  form  upon  Equation  (5) ,  but  should  be  fitted  with  experimental 
constants.     (Consult  further,  "  Applied  Mechanics,"  4th  Edition,  by  G.  Lanza, 
Art.  300,  on  the  Strength  of  Flat    Plates.     See    also    Engineering  News,  Vol. 
43,  pp.  10  and  162).     More  elegant  treatments  might  here  be  referred  to;  the 
intention  is  to  suggest  rather  than  to  solve  the  problem. 

59.  The  values  of  a  and  b  could  be  taken  somewhat  smaller  than  27  ins.  and 
48  ins.  because  the  bracket-angles  and  Z-bars  by  their  stiffness  and  riveting 
reduce  the  effective  values  of  a  and  b.     Moreover,  the  pressure,  47  5  Ibs.  per 
sq.  in.  is  high.     For  these  reasons  a  f-in.  side-plate  is  used.     Even  this  is  probably 
too  generous  and  bold,  and  designers  might  advocate  the  use  of  a  J-in.  plate. 
Local  boulders  can  at  times  produce  pressures  against  the  side-plates  and  cutting- 
edges   of  excessive  amounts  over  restricted   areas,   and   reasonable  provisions 
should  be  made  for  such  possibilities. 

60.  Side-Wall    Brackets — These   brackets   must    carry    their   portion    of    the 
sinking  weight  as  vertical  struts  and  must  resist  the  pressure  against  the  side- 
plates  as  cantilever   triangular  frames  supported  along  the  lower  chords  of  the 
roof-girders. 

61.  The  maximum  sinking  weight  has  already  been  fixed  at  14,500,000  Ibs.. 
Art.  48,  therefore  the  load  on  one  bracket  =  426,000  Ibs.     Allowing  a  compres- 
sion of  20,000  Ibs.  per  sq.  in.,  and    assuming    the  load  carried  wholly  by  the 
vertical  leg  of  the  bracket  requires  a  cross-section  at  that  leg  =21.3  sq.  ins. 
The  design  provides: 

2 — 6X4Xf-in.  angles  = 13.88  sq.  ins. 

1— 12iXi-in.  filler-plate  = 6.25  sq.  ins. 

Total 20 . 13  sq.  ins. 

In  addition,  as  reserve  strength,  we  may  count  to  some  extent  upon  the  side- 
plates,  the  ^-in.  bracket  web-plate  and  the  two  6X4Xi-in.  angles  on  the  inner 
inclined  flange  of  the  bracket. 

62.  In  designing  the  side-plates  it  was  concluded  that  a  maximum  pressure 
of  47.5  Ibs.  per  sq.  in.,  might  be  experienced  against  the  sides  of  the  working 


DESIGN    OF    A    RAILWAY    BRIDGE    PIER. 


19 


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20  DESIGN    OF    A    RAILWAY    BRIDGE    PIER. 

chamber.  'This  would  bring  upon  the  bracket  a  horizontal  load.  =  27,400  Ibs. 
per  lin.  ft.  of  vertical  leg.  Considering  the  bracket  as  a  cantilever,  the  resulting 
bending  moment  in  the  plane  of  the  roof-plates  of  the  working  chamber  would 
equal  7.5X27,000X3.75  =  769,000  ft.-lbs.,  while  the  horizontal  shear  for  the 
same  plane  would  be  207,000  Ibs.  The  bending  stress  in  the  vertical  leg  of  the 
bracket  is  a  tension  of  769,000  n-4.5  =  171,000  Ibs.;  and  in  the  inclined  leg  a 
compression  of  769,000  -3.7  =  208,000  Ibs.  The  tension  of  171,000  Ibs,  in  the 
vertical  leg  can  never  exist  because  that  leg  is  subjected  to  a  far  greater  com- 
pression from  the  pier  loads.  There  should,  however,  be  a  considerable  tensile 
strength  in  the  joint  between  the  end  stiffeners  of  the  roof-girders  and  the 
vertical  legs  of  the  working-chamber  brackets.  Allowing  20,000  Ibs.  per  sq.  in. 
compression  in  the  inclined  leg  requires  10.4  sq.  ins.;  two6X4Xl-in.  angles 
provide  13.88  sq.  ins.  The  horizontal  shear  of  207,000  Ibs.  at  the  top  of  the 
bracket  is  well  taken  care  of  by  the  two  6X4Xi-in.  angles  along  the  top,  to- 
gether with  the  further  stiffening  which  may  be  relied  upon  from  the  roof-plates 
and  lower  chord-angles  of  the  roof-girders. 

63.  The  £-in.  web-plate  of  the  bracket  has  an  effective  top  length  of  about 
48  ins.  and  a  net  shearing  area  of  about  18  sq.  ins.     At  10,000  Ibs.  per  sq.  in. 
the  shear  of  207,000  Ibs  for  the  horizon  of  the  roof-plates,  requires  20.7  sq.  ins. 
These  figures  would  indicate  a  weakness  in  shear  for  the  £-in.  web-plate;  it  is 
used,  remembering  that  the  pressure  of  47.5  Ibs.  per  sq.  in.  against  the  sides  of 
the  caisson   is   excessive.     To   strengthen   the  web-plates   against  buckling  it 
would  be  well  to  stiffen  them  along  lines  AB  and  BC,  Plate  3,  with  3  X  3  X  f-in. 
angles. 

64.  Side- Wall  Beams.     In  the  7  ft.  6  ins.  of  vertical  height  of  working  chamber, 
the  caisson  main  side-plates  are  reinforced  along  vertical  lines,  at  intervals  of 
4  ft.,  by  the  main  brackets.     These  side-plates  have  been  calculated  to  resist 
bulging  inward  by  considering  them  subdivided  into  rectangular  parts,   27  X 
48  ins.   each.      They  must    therefore  be  reinforced  along  horizontal  lines  at 
intervals  of  about  27  ins.     Two  lines  of  Z-bars  are  used  for  this  purpose.     See 
Plate  3.     Each  Z-bar  is  assumed  to  support  the  pressure  against  one-third  the 
height  of  the  working  chamber  or  a  load  of  6,830  X  2.5  =  17,200  Ibs.  per  lin.  ft. 
For  a  span  of  4  ft.,  this  load  gives  a  bendingmoment  =  34,400  ft.-lbs.  =  412,800 
in. -Ibs.,  which,  for  a  working  fiber  stress  of  20,000  Ibs.  per  sq.  in.,  requires  a 
Z-bar  whose  section  modulus  =  20.6;  a  6|X3f  X  J-in.  Z  gives  a  section  modulus 

=  16.4  and  is  used.  Again,  the  design  would  appear  weak.  The  Z  is  strength- 
ened by  a  3f  X  J-in.  filler  and  by  the  side-plates  and  the  pressure  or  load  used 
has  already  been  stated  as  generous.  Only  two  lines  of  Z-bars  are  needed.  At 
the  roof  of  the  working  chamber  the  side-plates  are  amply  supported  by  a 
6X6Xi-m-  angle  and  by  the  concrete  above  the  roof -plate.  At  the  cutting 
edge  the  extra  plates  and  a  6X6X  J-in.  angle  provide  sufficient  support. 

65.  Cutting-Edge.     It  is  not  possible  to  give  figures  for  the  design  of  a  cutting- 
edge.     Locally  where  a  boulder  is  encountered  the  stresses  may  be  enormous. 
Unequal  sinking  or  uneven  excavation  under  the  cutting  edge  may  produce  similar 
effects.     The  cutting-edge  often  may  be  badly  damaged  in  a  restricted  length 
and  require  repair.     It  must  be  stiff  and  tough  and  in  the  present  design  is 


DESIGN    OF    A    RAILWAY    BRIDGE    PIER. 


I? 

I 


22  DESIGN    OF   A    RAILWAY    BRIDGE    PIER. 

formed  by  reinforcing  the  J-in.  side-plates  by  two  plates,  each  18  ins.  in  depth, 
the  one  on  the  outside  £-in.,  the  one  on  the  inside  ^-in.  thick.  A  6x6X$-in. 
angle,  on  the  inside  and  slightly  above  the  cutting-edge,  adds  to  the  general 
stiffness.  This  angle  extends  continuously  about  the  caisson  and  supports  the 
lower  ends  of  the  side-wall  brackets.  Stout  timbers  bolted  to  this  angle  often 
further  reinforce  the  cutting-edge.  See  Plates  4  and  5. 

66.  Details.     Since  the  caisson  is  to  be  sunk  through  compact  silt  in  which 
few  boulders  occur,  no  great  precautions  need  to  be  taken  to  reduce  side  friction. 
Rivets  are  therefore  boiler-headed  on  the  outside  of  the  caisson.     In  bad  materials 
rivets  are  sometimes  countersunk  on  the  outside  and  water-jets  supplied   over 
the  imbedded  sides  of  the  foundation  through  holes    in    the   side    walls   (See 
Eng.  Record,  Nov,  23,  1893,  p.  410,  Foundations  of  the  East  Omaha  Bridge). 
Rivets  are  f-in.  in  diameter  throughout  and  the  pitch  so  far  as  possible  is  about 
3  ins.     The  caisson  is  to  be  thoroughly  calked  at  all  joints  to  secure  as  nearly  as 
feasible  a  water-tight  air-chamber.     Splice-plates  and  corner-angles  are  carefully 
considered  in  this  respect.     The  side-plates  are  spliced  vertically  every  8  f  t. , 
that  is,  at  every  other  bracket.     The  brackets  at  the  shorter  sides  of  the  caisson 
do  not  carry  as  much  load  as  those  against  the  longer  sides;  they  are  therefore 
somewhat  lighter,  (See  Plate  4).     Similar  remarks  should  apply  to  the  girders 
along  the  short  sides  of  the  caisson;  they  are  built  channel-girders  whose  webs 
are  the  main  side-plates. 

67.  Plates  3,  4,  and  5  give  all  the  important  detailed  features  of  the  caisson 
design.     Plate  6  shows  the  general  plan  for  roof-girders  and  bracket-framing; 
it  also  shows  the  positions  of  air-shafts  and  the  main  pipes  for  air,  water,  and 
sand-  or  mud-lifts. 

68.  A  caieful  bill  of  materials  for  the  steel-work  of  the  caisson  has  not  been 
prepared,  nor  could  it  be,  since  the  design  has  been  roughly  made.     The  amount 
of  steel  in  the  caisson  is  about  305,000  Ibs.     The  volume  of  caisson  from  cutting- 
edge  to  top  of  side-plates  is  22,480  cu.  ft.     The  metal  weight  therefore  is  13.5 
Ibs.  per  cu.   ft.   of  volume.     The  assumed  weight,  in  discussing  the  caisson's 
flotation,  Art.  41,  was  269,000  Ibs.,  a  considerable  smaller  quantity,  but  it  will 
be  at  once  noted  that  the  discrepancy  in  no  way  seriously  affects  the  design. 
Our  caisson  is  heavier  than  an  average  example,  partly  because  of  the  depth  of 
foundation ,  and  partly  because  the  design  is  uniformly  conservative,  using,  as 
has  been  repeatedly  noted,  high  values  for  the  stress-producing  loads  and  forces. 

XIV.     COFFER-DAMS,  SHAFTS,  LOCKS,  AND  POWER  PLANT. 

69.  The   permanent   coffer-dam,    detachable   coffer-dam,    the   air-shafts   and" 
locks  for  material  and  men,  supply-pipes  to  the  caisson  for  air  and  water,  sand- 
lifts,  mud-pumps,  etc.,  are  only  shown  in  outline.     See  Plates  2,  6,  and  7.     These 
parts  of  the  structure  have  been  sufficiently  considered  by  the  writer  to  make  an 
approximate  estimate  for  the  complete  cost  of  the  pier,  but  it  is  regretted  that 
time  was  not  available  to  develop  further  their  design  in  these  pages. 

70.  The  power  plant,  the  equipment  and  methods  for  sinking  the  foundation, 
the  anchoring  and  guiding  of  the  structure  during  its  descent,  the  handling  of 
the  men,  the  physiological  effects  of  compressed  air  upon  the  workmen,  and 
many  other  important  matters  can  here  be  stated  in  closing  this  article. 


DESIGN    OF    A    RAILWAY    BRIDGE    PIER.  23 

XV.     BILL  OF  APPROXIMATE  COSTS. 

71.   Pier  below  mud-line. 

1.  Concrete  below  cutting-edge  =  675cu.  yds.  at  $12 $  8,100 

2.  Caisson  steel  =  305,000  Ibs.  at  3.5  cts 10,700 

Concrete  =  510  cu.  yds.  at  $12.00 

320  cu.  yds.  at      8.50 8,845 

3.  Permanent  coffer-dam: 

Timber  =  150  M.  ft.   B.    M.,   at  $40 6,000 

Metal:   bolts,  spikes,  etc.,  =  22,500  Ibs.  at  3  cts 675 

Concrete  =  2,200  cu.  yds.  at  $8.50. 18,700 

Shafts,  pipes,  etc..  =  36,480  Ibs.  at  3.5  cts 1,280 

4.  Sinking  cost  =  138,130  cu.  ft.  displacement  at  20  cts 27,900 

5.  Detachable  coffer-dam: 

Timber,  101  M.  ft.  B.  M.  at  $40 4,040 

Ironwork  =  15,100  Ibs.    at  3  cts 450 


Total  cost  of  foundation  below   mud-line, $86,690 

Foundation  volume  below  mud-line  =  3,490  cu.  yds. 
Cost    of    foundation  below   mud-line,  iri eluding  detachable 
coffer-dam  =  $24  85  per  cu.  yd. 

72.     Pier  above  mud-line: 

6.  Coping  =  49.5  cu.  yds.  at    $40 $  1,980 

7.  Limestone   ashlar  =  1,625  cu.  yds.  at  $15 24,375 

8.  Concrete  =  1,450  cu.  yds.  at    $6.50 9,425 


Total  cost  of  pier   above  mud-line $35,780 

Pier  volume  above  mud-line  =  3,125  cu.  yds. 
Cost  of  pier  above  mud-line  =  $11.40  per  cu.  yd. 
Total  volume  of  foundation  and  pier  =  6,615  cu.  yds. 

Total  cost  of  foundation  and  pier $122,470 

Cost  of  foundation  and  pier,  =  $18.50  per  cu.  yd. 

73.     In  the  above  estimate  the  following  prices  were  used: 
Concrete  under  cutting-edge  at  $12  per  cu.  yd. 
Caisson  concrete  at  $12  per  cu.  yd. 
Caisson  steel-work  at  3.5  cts.  per  Ib. 
Yellow  pine  for  coffer-dams  at  $40  per  M. 

Excavating   and    sinking  at  20  cts.  per  cu.  ft.  displacement   below  low- 
water  line. 

Permanent  coffer-dam  concrete  at  $8.50  per  cu.  yd. 
Hardware  in  coffer-dams,  150  Ibs.  per  M.  at  3  cts.  per  Ib. 
Limestone  ashlar  masonry,  f-in.  joints,  at  $15  per  cu.  yd. 
Pier  concrete  above  mud-line  at  $6.50  per  cu.  yd. 
Granite  coping  at  $40  per  cu.  yd. 
Steel  in  air-shafts,  left  in  work,  at  3.5  cts.  per  Ib. 


24  DESIGN    OF    A    RAILWAY    BRIDGE    PIER. 

XVI.     REFERENCES. 

1.  Baker,  I.  O.;  A  Treatise  on  Masonry  Construction. 

2.  Patton,  W.  M. ;  A  Practical  Treatise  on  Foundations. 

3.  Fowler,  C.  E. ;  Ordinary  Foundations,  Including  the  Coffer-dam  Process 

for  Piers. 

4.  Engineering  Record,  June  17,  1893,  p.  38,  vol.  27; 

Pneumatic  Caisson  for  Seventh  Avenue  Bridge,  New  York  City. 

5.  Engineering  News,  vol.  13,  1885,  pp.  14,  41,  63,  83,  122,  228,  244.,  262,  274; 

Foundations,  Havre  de  Grace  Bridge. 

6.  Morison,  G.  S. ;  The  River  Piers  of  the  Memphis  Bridge; 

Proc.  Inst.  C.  E.,  vol.  cxiv,  p.  289. 

7.  The  Forth  Bridge  Report. 

8.  The  Memphis  Bridge  Report. 

9.  The  St.  Louis  Bridge  Report. 

10.  Railroad  Gazette;  Jan.  13,  1893,  p.  19.  vol.  13; 

Seventh  Avenue  Drawbridge. 

•  11.   Engineering  Record;  Nov.  23,  1893,  p.  410;  Construction  of  Pivot  Pier, 
Interstate  Bridge,  Omaha,  Neb. 

12.  General  Specifications  for  Bridge  Substructures;  The  Osborn  Co. 

13.  The  Hawkesbury  Bridge. 

14.  The  New  East  River  Bridge. 

15.  The  New  York  and  Brooklyn  Bridge.  ,, 

16.  Engineering  News;  Dec.  7,  1893,  p.  458;  Pneumatic  Foundations  for  the 

Manhattan  Life  Building,  New  York. 

This  list  does  not  presume  to  be  complete  nor  does  it  intend  to  give  all  of  the 
best  and  most  important  references.  The  writer  has  given  references  at  his 
immediate  command  without  seeking  to  make  the  table  exhaustive.  It  will 
help  the  student  to  find  other  articles  relating  to  the  subject. 

Computations  have  been  made  with  the  aid  of  a  slide-rule.  The  arithmetic 
is  not  exact.  Errors,  it  is  believed,  are  far  within  one  per  cent,  and  therefore 
more  than  small  enough  for  a  first  study  and  estimate. 


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UNIVERSITY  OF  CALIFORNIA 
DEPARTMENT  OF  CIVIL  ENGINEERING. 

STRUCTURAL  ENGINEERING 

I 


NOTES  ON  FOUNDATIONS  ANfl  MASONRY  STRUCTURES 
COURSES  113  -  114. 


By 

Charles  Derleth,  Jr. 

ll 


Revised  and  Enlarged  From  Earlier  Editions 
Berkeley,  California,  October  1,  1921. 


J 


-  --••"- 


-^  I 't*.U --:-. 

- 


TABLE  OF  CONTENTS 

)  -" 

FOUNDATIONS. 

Part  1. 
Explorations   —  •  Shallow  Foundations. 

Chapter  1.  Examinations  and  Explorations .  .  ,  .   ,  ......  I 

1.  Digging  Test  Pits  . 2 

2.  Driving  Pipes  or  Solid  Iron  Bods  ......  2 

3  ,  Borings  with  Post  Diggers  end  Augers  . .. .  .  .  .  4 

Sather  Tower  ...................  .  ....  5 

Calaveras  Dam  .  .  .  .  .........  .  .  ,  ......  6 

4.  Test  Piles  ...........  .  ......  8 

Harbor  Development  at  South  San  Francisco   ........  9 

Oalcland  Auditorium.    ......../.• 12 

Calaveras  Dam  ..............  13 

5.  Borings  v.'ith  the  Sand  Pump   ... *   .  W 

Civic  Center,   San  Francisco 15 

6.  Sinking  with  \Vr.ter-Jet 16 

7.  Drilling  v/ith  Artesian  \7ell  Boring  Tools 18 

8.  Drilling  with  the  Diamond  &  Stoel     Shot  Drills 20 

General  Precautions   for   Test   Borings ..21 

Sub-Aqueous  Borings , "33 

References '*..££ 

Problems 27 

Chapter  2.  Classific£.tion  of  Foundation  Soils  -  Bearing  Power   ......  28 

1.    Solid  Rock 29 

•2.  Gravel  and  Kardpan  ........................  31 

3.  Sand  ..........  ...............  32 

4.  Clay .  .  . .  35 

5.  Ordinary  Soil  »•  Earth  Pressure.  ............  .t .  ...  35 

6.  Semi -Liquid  Soils,  «•  Quicksand .  ~58 

Methods  of  Increasing  the  Bearing  power  of  Earth  Foundations  ......  42 

Drainage  and  Confinement  .....................  42 

Sand  Piles  ..................... .  '43 

Stock  Ramming  «  ...................  44 

Sand  Layers '.  .  .  44 

Testing  the  Bearing  Power  of  Soils  ....................  45 

Pressures  on  Foundation  Beds  »•  Abnormal. Pressure 47 

Examples  of  Pressures  on  Foundations  and  Boundation  Beds  in 

Sand  and  Ear.-th  ..'.«........»...,... 47 

Summary  -  Foundation  Soils:  Their  Supporting  Cape  city  » 49 

References;  Foundation  Soils  and  Pressures  ...  .......  49 

Problems  ..*.......................  .  .  50 

Chapter  3.  Classification  and  Requirements,  Foundation  Designs  ......  51 

A.  According  to  the  Material  Upon  7,/hich  the  Foundation  Rests  .  .'  ,   51 

B.  According  to  Tjrpe  of  Structure  Designed  ,,,,..     ,  ...  .51 

Foundation  Requirements  .....'...................  .51 

References  -  Specifications  -  Problems  ..................  53 


ii 

Chapter  4,   Distribution  of  Foundation  Pressures  -  Spread  Footings,        ...  54 

Table  -  "/eight   of  Masonry  , . „    .  55 

Table   -  live  Loads  for  Buildings 56 

Center  of  V/eight  Vs.   Center  of  Figure   for  Building  Footings  .......  57 

Table  -  V/all  Thickness t    ............  58 

Eccentric  Foundation  Loads    .*.....    4   .'...»......»......  58 

Treatment  for  Center  of  Pressure  "./ithout  tlie  lliddle   Third  .......<,  61 

Pressure  on  the   Foundation  Bod  of  a  Ifesonry  Pier   .............  62 

Stability  Against  Sliding  .............    .^  t   .........  64 

Spread  Footings   .    ...  :;    ............ 66 

1.  Timber  Footings    ,    .    . .66 

2.  Masonry  Offsets,   Rubble ;Brick  or  Concrete    ..............  67 

Table  Shov.'ing  Offsets   for  i-Iasonry  Footing  Courses   .........  68 

3.  Timber  Grillages   or  Rafts ,    .    .    . 71 

4.  Inverted  Arches   of  Stone,   Brick,  Concrete  or  Reinforced  Concrete.  72 

5.  Footings,  of  Structural  Stec-1  Beams  and  Concrete    , 73 

Cast  Iron  Bases,   Steel  Pedestals,   etc 76 

Other  Design  Llethods   for  Steel  Grillage  Footings 77 

6.  Footings  of  Rejnforced  Concrete  Slabs    79 

V/all  Foot  ings,.  Bear  ing,   Shear 79 

Bending, Design  for  Reinforcement .80 

Interior  Column  Foot  ings,. Bearing,   Shear,.  Bend  ing 81 

General  Comment  on  the  Design  of  Footings  Under  Interior  Columns  82 

7.  Combined.  Footings 83 

Call  Building,  San  Francisco 84 

Washington  jlonument ......  .84 

Singer  Building  Foundati  on .  .86 

Trapezoidal  Combined  Footings   .................   87 

Combined  Footings  of  Structural  Steel  I-bea'ms  and  Core  re te  .  .  .90 
Tvvo  Unequal  Column  Loads  Supported  upon  a  Rectangular  Grillage  91 
Two'  Unequal  Column  Loads,  the  Greater  Load  at  the  Lot  Line, 

Supported  upon  a  Trapezoidal  Grillage  of  two  ffiers  of  ffieams  93 
Three  or  More  Unequally  Loaded  Columns.,  in  One  Line,,  Unequally 

Spaced,  Supported  upon  a  Rectangular  Slab 95 

Partial  Application  of  the  Principle  of  Three  .'.foments.  ....  97 
Eccentric  Steel  Beam  Grillage  Foundations,  Native  Sons 

Hall,  San  Frcncis  co - 99 

Cantilever  Spread  Footings  of  Reinforced  Concrete  100 

References,  Problems  ....  101 

Chapter   5.   Sheefr  Piling 104 

Light  Wooden  Sheet  Piling 104 

Effect  of  Cohesion 107 

Heavy  Wooden  Sheet  Piling 109 

Steel  Sheet  Piling  .............' •    • 

Requirements   for  Metal  Piling  .....    114 

Spacifi  cat  ions    for  Steel  Sheet  Piling 115 

Reinforced  Concrete  Shoot  Piles    ....    116 

Hennobicue  Shoot  Piling  ,   Fig. .55  

Reinforced  Concrete  Sheet  Piling;  U.S. Naval  Coal  Depot,   Tiburon, Calif. . 

Extracts   from  the   Specifications « •    •    H"7 

Extracts   from  the  Specifications  for  Pile  Driving  

Concrete  Sheet  Piles   for  Docks   

An  Analytic  Problem  . • 

The  General  Case.,   Continuous  Spans .• 

Simpler  Case,    for  One  Continuous  Span I23 

Practice!  Case,  One  Simple  Span 124 

Additional  References;   Problems   ....    •    


ill. 

Chapter  6,  Bearing  Piles „ 127 

Introduction  , 


Timber  Piles,   Timbers  Available    ............  °129 

Specifications   for  Timber  Piles    ........  129 

Preparing  Piles    ..............,..]  '.'.130 

Driving  Piles,    •   ••.••...«..........  ,151 

Pile  Hammers ........        .    .    .    .  133 

Sinking  Piles  by  Water  Jet   , .    .    .    .    .  .1^5 

Bearing  Power   Of  Piles   .............].]  ]  *156 

l.r/here  Driven  to  a  Fir.i  Bottom.    ...........  .    .    .    „    .    136 

2,  ?/here  No  Bottom  is  Ree.ciied  .    ,    .    „    .    .    .    .    „    .  156 

Example   ...,...'.....;....,...„......      157 

3.  Usual  Pile  Formula  .  .  .  . , .  .   137 

Special  Pile  Formulae  .........................  141 

Table  by  J.Foster  Crowell  ...............   ..!.,..  142 

Specified  Loads  for  Piles,  Details,  General  Remarks  .  .  .  .     .  .  .  .  143 

Preparation  of  Pile  Tops,  Capping  of  Piles  ..............  146 

Piles  in  Soft  Ground  ............  „  .......  „  .  ...  148 

Effect  of  Lagging  on  the  Bearing  Power  of  Timber  Piles  ........  .149 

Screw  Piles  .......;.,........'.............  151 

Disk  Piles  .  .  .  .......  .  .  .  .  .  .  .  .  .  .  .  „  .   ....;.  153 

Protected  Piles  ...*.............».........  153 

Chemical  Preservatives  for  Timber  .  .  .  .  .  ..  ,  .  .  .  .....  '.  .  .  .  154 

Protected  Pile  Clusters  .  .  .  .  .........  .  ...„.„..  .  .  157 

Protected  C^/linder  Pile  (Howard  C.  Holmes ,  Pctent  Kol92006lO> 159 

Sumnary  .',,......... 160 

Additional  References  .......  ,%  .........  i  ........  1601 

Problens  -  Bearing  Piles  ...............  ^  ....  V  ......  .161 

Chapter  7,  Concrete  and  Reinforced  Concrete  Piles  .............  163 

Their  Advantages  and  Disadvantsges  .  .  .    ..............  .163 

Classification  -  Concrete  Piles  ....................  165 

1,  Piles  Loaded  in  Piece,  .  .  .    ................   165 

Raymond  Piles  ........................  165 

Simples  Piles  ...............  ^  .....>..  167 

Clark  Piles  .......  «  .......  .  .........  168 

Abbott  Piles o  ...:...  ^  ................  168 

2,  Piles  Molded  and  Then  Driven  .:.........   .....  .170 

Hennebicue  Piles  ......................  171 

Corrugated  Piles 171 

Cole  Piles  ......   ..................  172 

Specifications,  Reinforced  Concrete  Pile  .  ........  .173 

Protection  of  Embedded  Steel  end  T'ood-.    ...............  175 

References,  Concrete  Structures  Exposed  to  Sea  T7rter(£o£  1-17.)  ....   176 

Concrete  Piles,  References  Kos.  18-22  ............  v  .  .176 

Problems  .  '„  ..............  ..........  .......  177 

£uRT  II,  FOU1'H'.TIO:;S  UhDLH  '7..TLR. 

C hr.pt er    8.  Concrete  Deposited  Under  V/ater    .........   i    .......    178 

Examples   of  Concrete  Deposited  Under  r/cter    ..............    180 

1.  Concrete  Deposited  by  Chute.    ....    o    ............   180 

Tremie  Concrete    ..............    .    ,    .    ,    .    .    .    .    .    .182 

2,  Concrete   Deposited  by  Bucket .    .    183 

Lr.itr.nce    ..........................    184 

Additional  References   ..«.....,*.*«*.>• 185 


iv. 


.Chapter   9.  Coffer   Dz.:is       ..*.,.,..        ..........  186 

Pivot   Pier,  Harlem  Ship  Cr.nr.l   Bridge   ......  .  .  186 

Variations  of  'c"::3  Confer  Bar-  Process   •    .„»......  .  190 

Pivot  Pier,    Seventh  Ave.   3v/ing  Bridge,  Few  York  City  ...,...».  191 

Dumbarton  Bridge  Foundations   ....'........        ,    .    .    .    .        .    .  191 

Additional  Eefererjces    ......  <,-........„.....  , .  192 

Chapter  10.    Open  Caissons    .   .    .    .    .        .....................    193 

Pier  III,  Harlem  Ship  Canal  Bridge,   lev/  York  City   .   .        .    .  .'-...    194 

Open  Caisson  Supported  on  Piles      ................    ^  .,    196 

Additional  References    ........  ^'.   .............    0    ...   .197' 

Chapter  11.  Pneumatic  Caissons.    ...........        .........    »198 

History  of  the  Pneumatic   Process   .....>.......'.......    199 

Pneu:-.r..tic  Piles    ...........................      199 

Vacuum  Process   ..*««..;.......;.*...„......,   199 

Plenum  Process   .............................   200 

Caisson  Design  arc1.  Operation  .....................    201 

Sinking  Weight    .........................      203 

Caisson  Flotation   .   .   .    .   .     ......    c    ............    205 

Sinking  Caisson   .      .......................     203 

Excavating  Lifts  and  Pumps    ....«..'.......'.....    ,204 

Physiological  Effects    of  Compressed  Air;  Precautions   in  Kriidling  Hen,,    204 
Caisson  Concrete    ,    =    0.0.......................    205 

Crib  ",'ork  aix1.  Coffer  Darn  .......................    205 

Sew  East  River  Bridge    ........................     206 

Seventh  Avenue  Swing  Bridge,  Eew  York  City   ...*......*....    206 

Additions.1  References   ........................     207 

Chapter   12.   Deep  Well  Dredging   ...........        .        .00......   209 

Pougl-keepsie  Bridge,  Rev;  York,   OJtniber  Crib  Well   ...........    .209, 

East  Omaha  Bridge,   Ilissouri   River;  I.Ietr.1  Caisson  ...........   209 

Efewkesbury  Bridge,  Kev;  South  Wales    ..................  216 

Concrete  Caisson  Spillway,   Calaveras  Dam,   Spring  Valley  Water  Co.    .    „      216 
Additional  References    .«.....................*•  219 

Chapter   151  Deep  Foundation  Pressures    ..................    .220 

References   .....    ,'.........».«..'.%.    ...•«»..  220 

Analysis    ..........    ^    .        .    .    .    .    .    .    .    .    .    .........    221 

Additional  References    .........................    225 


FOUNDATIONS  AJM'D  MASONRY  STRUCTURES 

1 

Chapter  I. 

EXAMINATIONS  AND  EXPLORATIONS 

Structures  of  great  weight  and  height  usually  give  rise  to  difficult 
foundation  problems.  The  design  of  proper  sub-structures  for  high  office  buildings 

,x 

and  bridge  piers,  when  founded  in  treacherous  material,  often  will  present  serious 
cases.  Before  attempting  the  design  of  any  important  sub-structure,  careful  exam- 
inations and  explorations  should  be  made  of  the  mass  of  material  in  or  on  which 
the  work  is  to  be  founded. 

In  many  engineering  projects  soil  examinations  are  as  necessary  a  part 
of  the  preliminary  study  as  are  surveys  and  office  computations.  Results  obtained 
from  testing  foundation  soils  may  materially  influence,  not  only  the  foundation 
design  of  important  structures,  but  even  their  location.  A  conservative  and 
thorough  engineer  will  insist  on  having  the  time  and  funds  available  for  obtain- 
ing ample  and  accurate  data  regarding  the  character  of  foundation  material  before 
proceeding  v/ith  design  or  construction,  sometimes-  even  before  finally  deciding  on 
location.  In  many  important  bridges  the  cost  of  the  sub-structure  may  approximate 
or  exceed  that  of  the  super-structure;  that  is,  may  be  one-half  or  more  of  the 
total  cost.  As  favorable  soil  conditions  may  affect,  very  largely,  savings  in 
the  cost  of  the  sub-structure,  a  final  choice  of  bridge  site  and  truss  type  may 
be  influenced  mainly  by  the  results  of  foundation  examinations.  When  the  site  of 
a  structure  is  definitely  assigned  beforehand,  as  for  city  buildings,  a  careful 
examination  of  the  soil  becomes  particularly  important,  since  the  general  design 
and  scheme  of  foundation  and  thus  that  of  the  entire  super-structure  may  depend 
upon  the  exploration;  for  example,  the  site  may  require  piles  instead  of  footings. 
It  is  usually  inadvisable  to  proceed  with  a  design,  and  still  more  so  with  the 
actual  execution  of  any  important  structure  until  adequate  tests  have  completely 
and  accurately  determined  the  character  of  foundation  material. 


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The  methods  pursued  for  making  examinations  will  vary  greatly  with  the 
character  and  condition  of  the  subsurfacd  material  and  the  depths  to  be  reached. 
They  may  be  classified,  in  general,  under  eight  principal  headings,  depending 
chiefly  on  the  type  of  the  implements  used. 

1.  Digging  test  pits 

2.  Driving  pipes  or  solid  iron  rods 

3.  Boring  with  post  diggers  and  augers 

4.  Test  piles 

5.  Sand  pump  borings,  either  with  or  without  casing 

6.  Sinking  pipes  by  water- jet 

7.  Drilling  v/ith  artesian  well  tools 

8.  Diamond  drill  and  steel-shot  drill  borings 

!•  Digging  Test  Pits.  This  method  is  used  for  important  structures 
where  the  strata  are  of  uncertain  character  and  the  foundation  bed  is  at  no  great 
depth.  It  is  slow  and  expensive  so  that  it  is  usually  employed  only  when  the  exact 
location  of  the  proposed  structure  has  been  determined.  Pits  are  dug  from  4  or  5 
to  10  or  12  feet  square,  preferably  to  the  depths  to  which  the  actual  foundation 
•will  reach,  requiring  in  many  locations  constant  pumping  to  keep  the  pits  from 
flooding  by  percolating  water.  The  great  advantage  6f  this  work  is  that  it  shows 
the  strata  penetrated  in  their  natural  position  and  character,  convenient  for  any 
examination  desired.  If  the  pits  are  deep,  it  may  be  necessary  to  use  heavy  timber 
bracing  and  lagging,  just  as  in  actual  foundation  pits  or  trenches  to  prevent  the 
sides  from  caving.  The  construction  of  this  sort  of  bracing  is  discussed  in  later 
articles  (consult  sheet  piling  and  coffer-dams).  The  method,  while  costly,  is 
jnore  satisfactory  and  certain  than  any  other  and  has  been  used  extensively  for 
important  buildings  and  dams.  It  is  frequently  possible  to  locate  test  pits  to  form 
a  portion  of  the  permanent  excavation  so  that  the  labor  of  digging  them  is  not 
entirely  lost. 

2.  Driving  Pipes  or  Solid  Iron  Rods.  This  is  a  common  method  for  shallow 
or  unimportant  work.  It  is  used  satisfactorily  to  determine,  for  long  trenches, 
such  specific  information  as  the  depth  to  rock  or  gravel.  Data  secured  in  this  way 
are  oftea  sufficiently  reliable  to  fix  the  grades  of  sewers  or  drains  or  to  enable 


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contractors  to  bid  intelligently  on  trench  work.   Solid  iron  rods  or  pipes  from 
3/4"  to  1.5"  in  diameter  can  be  driven  in  ordinary  soils  from  10  to  40  or  50  ft. 
by  repeated  blows  with  a  maul,  the  rods  or  pipes  being  constantly  turned.  As 
ordinary  water  pipe  will  not  stand  much  driving  it  is  best  to  use  double  strength 
pipe  with  hydraulic  couplings.  These  couplings  extend  beyond  and  protect  the  pipe 
threads.  They  also  allow  the  sections  of  pipe  to  be  screwed  up  till  their  ends  abut 
at  coupling  centers.  When  the  pipes  can  be  pulled  at  intervals  they  usually  bring 
up  samples  of  the  material  to  be  found  at  the  bottom  of  the  test  hole.  If  either 
solid  rods  or  pipes  are  used  it  is  best  to  upset  them  at  the  lower  end,  in  order 
to  decrease  the  friction  of  the  sides  while  driving.  The  information  obtained  by 
this  method  is  rather  .neager  and  liable  to  lead  to  erroneous  conclusions.  It  is 
difficult  to  distinguish  the  different  strata  except  rocic  and  gravel.  It  is 
difficult  to  penetrate  compact  formations,  especially  sand  and  gravel.   In  order 
to  force  a  line  through  gravel  it  is  usually  necessary  to  use  at  the  lower  end 
a  chisel  bit  of  hardened  steel,  and  to  rotate  the  apparatus  constantly.  Boulders, 
logs,  roots  or  other  obstructions  may  cause  the  rod  to  glance  and  wander,  or  the 
pipe  to  split.  More  commonly  they  will  stop  the  driving  altogether  and  th$s  may 
be  mistaken  for  solid  rock.  A  number  of  holes  rather  close  together  should  be 
driven  before  definitely  concluding  that  solid  rock  has  been  reached.  Y/hen  a 
foundation  bed  profile  plotted  from  these  drivings  shows  erratic  features,  it  is 
wise  to  question  the  results  and  to  resort  to  further  investigation,  either  by 
driving  additional  rods  or  pipes  or  by  selecting  a  more  reliable  method  of 
examination. 

The  method  is  used  more  for  obtaining  negative  than  positive  results.  If 
solid  rock  is  desired  for  the  foundation  of  an  important  structure,  it  is  seldom 
safe  to  rely  upon  information  obtained  in  this  way.  If,  however,  a  contractor  seeks 
the  probable  average  depth  to  rock  in  a  proposed  sewer  trench  in  order  to  guide 
him  in  estimating  a  unit  cost  for  the  work,  errors  -nade  by  this  method  of  testing 
may  not  "be  so  serious  since  they  are  apt  to  be  on  the  scfe  side.  The  method  is 


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inexpensive  and  requires  little  equipment;  therefore  it  may  be  advantageously 
used  as  a  preliminary  toamore  thorough  program  while  the  results  obtained  may 
indicate  locations  where  it  is  advisable  to  make  other  tests,  or  may  assist  in  the 
choice  of  final  methods  for  continuing  the  exami nation. 

3.  Borings  With  Post  Diggers  and  Augers.   This  is  a  safer  method  than 
the  preceding,  especially  in  compact  soils.  Samples  of  clay  or  other  stiff  material 
can  be  brought  up  from  a  great  depth  and  satisfactorily  examined,  though  they  will 
be  somewhat  more  consolidated  than  in  their  natural  state.  If  very  loose 'or  wet 
surface  soil  is  encountered  it  may  be  necessary  to  encase  the  top  of  the  hole  by' 
driving  light  boards,  (sheet  piling,  Chapter  V),  or  iron  or  terra  cotta  pipe.  The 
holes  may  be  2  to  6  inches  in  diameter  and  may  be  illuminated  by  reflecting  sun- 
light into  them  by  means  of  small  mirrors. 

Tools.  A  heavy  carpenter's  auger  can  be  used  for  shallow  borings.  For 
deeper  work,  steel  prospecting  augers  may  be  made  by  twisting  rectangular  bars  of 

• 

steel  1/4  to  1/2  inch  by  3  to  6  inches  and  3  to  6  ft.  long.  The  stem  is  made 
either  from  pipe  or  solid  rods,  sdrewed  or  locked  together  in  sections  5  to  20  ft. 
in  length.  A  good  stem  can  be  made  of  double  strength  pipe  1  to  2  inches  in  diam- 
eter, preferably  with  hydraulic  couplings,  provided  with  keys  to  prevent  unscrewing 
The  top  section  may  be  square  with  a  specially  provided  wrench  (see  Fig.  1)  for 
turning,  or  the  wfeole  apparatus  may  be  easily  tux-ned  with  pipe  wrenches.  It  is 
extremely  difficult  to  bore  through  compact  sand  or  grsvel.  Narrow  strata  of  gravel 

can  be  penetrated  by  substituting  a  chisel  bit  for  the  auger,  churning  the  vhole 

rapidly 
apparatus,, up  and  down.  If  the  holes  are  more  than  12  to  15  ft.  deep,  a  derrick 

should  be  used  with  a  block  and  tackle  or  windlass  to  re ise  the  auger.  A  simple 
three-legged  derrick,  or  a  two-legged  derrick  with  guy  ropes  (see  Figs.  2  and  4) 
will  suffice.  Care  should  be  taken  not  to  bore  too  deeply  before  raising  to  the 
surface.   By  coupling  the  stem  and  casings  in  sections  ecch  time  the  auger  is 
lowered.,  depths  of  100  ft.  or  more  can  be  reached.  As  the  auger  usually  sinks 
easily  "by  its  own  -Height  but  Is  difficult  to  raise,  especially  in  compact  : 


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formations,  if  its  stem  is  marked  each  time  it  is  let  down  into  the  hole,  one  can 
prevent  the  tendency  to  go  too  far  each  time.  For  shallow  holes  5  to  15  feet, 
common  post-hole  diggers  6  to  8  inches  in  diameter  may  be  used  advantageously 
if  the  material  is  stiff  enough  to  prevent  the  holes  caving  in  from  the  sides. 
:  '  •.:        Ha*£§.lL  Tower 

Examinations  for  the  Sather  Tower  foundations,  University  of  California, 
were  made  by  hand  boring,  using  the  heavy  tools  just  described  (see  Figs,  2,3,4). 
This  Tower  consists  of  a  steel  frame  with  reinforced  concrete  floors  and  curtain 
walls,  the  concrete  wall  backing  being  faced  with  granite  and  marble.  The 
structure  is  302  ft.  high  with  a  base  plan  34  ft.  square  at  the  ground  line.  Its 
16  columns  penetrate  the  ground  to  elevation  -10  ft. ,  where  their  steel  shoes 
rest  upon  a  grillage  consisting  of  two  tiers  of  24"  80#  I-beams;  12  beams  in  each 
layer.  (See  Fig.  4A).  The  steel  grillage  is  imbedded  in  a  solid  slab  of  concrete 
48  ft.  square,  8  ft.  thick,  the  lower  4  ft.  tinder  the  steel  beams  being  reinforced 
for  shear  and  bending  stresses.  The  foundation  bed  is  at  elevstion  -18  ft.  The 
total  dead  and  live  weight  resting  upon  this  level  is  13  760  000  Ib. ,  or  5950  Ib. 
per  sq.  ft. ,  neerly  3  tons.  A  wind  pressure  of  20  Ib.  per  sq.  ft.  produces  an 
overturning  moment  =  25  000  000  ft.  Ibs.  ,  and  a  pressure  transfer  of  1360  Ib. 
per  so,  ft.,  or  a  maximum  qf  7310  Ib.  per  sq.  ft.  =  3.6  tons.  With  a  30  Ib.  wind 
the  similar  figures  are  2040  Ib.  per  so.  ft.;  7990  Ib.  per  sq.  ft.,  and  4  tons. 

Five  borings  were  made;  three,  Kos.  1-3-4,  being  stopped  by  boulder 
obstructions  at  the  relatively  shallow  depths  of  20,  18  and  29  feet;  (see  Fig.4B); 
while  borings  Hos.  2  and  5  penetrated  each  63  ft.  The  material  traversed  in  all 
cases  is  gravelly  clay  with  boulders.  Borings  INOS.  2  and  5  probably  struck  sand- 
stone. 

Until  the  complete  exccvations  for  the  foundation  were  made,  the  engineers 

were  uncertain  whether  holes  Kos.  1,  3  and  4  were  stopped  by  boulders  or  by  solid 
rock.  It  was  possible  therefore  that  bedrock  at  the  site  shelved  rapidly  or  con- 
a  precipice- 


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With  v/ell  boring  tools  or  the  diamond  drill  such  uncertainties  would 
vanish.  In  this  case  hand  boring  apparatus  was  selected  b  ecaiE  e  the  price  bid  was 
90  cents -per  ft.,  while  for  power  machines  the  minimum  charge  asked  was  &300. 
for  100  ft.  or  less  and  £>2.50  extra  per  linear  foot  for  total  length  of  holes 
drilled  exceeding  100  ft.  Considerable  was  known  about  foundation  material  in 
the  immediate  vicinity  through  earlier  building.  The  records  obtained  left  the 
exact  levels  of  rock  bed  uncertain. 

• 

Calaveras  Dam. 

In  March  1918  the  Calaveras  Dam,  Spring  Valley  Y/ater  Company,  failed. 
The  upstream  toe  was  pushed  into  the  reservoir  by  the  presaire  of  the  liquid 
clay  core-  In  order  to  repair  the  damage  it  became  immediately  necessary  to 
study  the  character  of  the  material,  not  only  in  those  portions  of  the  dcm  which 
did  not  move,  but  also  in  the  embankments  which  did. 

In  the  softer  clay  portions  hand  augers  inside  steel  casings  were  used 
for  a  number  of  test  1-oles.  These  were  sunk  with  difficulty  because  the  clay 
contcined  many  stones  e.nd  rock  fills  which  had  sloughed  from  the  toes  into  the 
liquid  central  core  during  the  building  of  the  dera  and  also  at  the  time  of  the 
failure.  The  following  is  the  log  of  well  No.  15.  Sand  pumps  were  used  to  lift 
churned  material  from  the  well. 

\7ell  KQ_.  15;  Drilling  Log;  Hand  Rig_  C_. 

Final  location  co-ordinates  =  XXXIV  +  44,  23  +  45;  elevation  661.4 

Note:  This  v/ell  is  near  two  test  pits  dug  on  June  6,  1918,  end  is 
surrounded  by  test  piles  Kos.  23,  24,  25,  end  26. 

June  12,  1918,  second  location. 

0  -  8  ft.  flowing  clay 

8  -  9.5  ft.  clay  end  stones 

9.5  -  1C  ft.  solid  rock,  drilled 

•  10-13  ft.  rock  fill,  herd  packed. 

At  13  ft.  encountered  large  boulder;  driller  decided  to  move  to  new 
location. 


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7. 
June  14,  1918,  third  trial. 

0-10  ft.     liquid  clay 

10  -  29  ft.     rock  fill.  Big  boulder  at  23  ft.  Used  12.5  ft. 
of  10"  casing,  then  changed  to  6"  casing. 
Material  exceptionally  clear  of  mud  and 
stands  up  well.  Water  at  surface  of  ground. 
Driller  had  to  throw  clo$.s  of  clay  into  well 
to  bring  up  stones  on  auger.  Casing  sometimes 
3  ft.  behind  bottom  of  hole.  The  6"  casing 
became  jammed  between  29  end  30  ft.  and 
could  not  be  driven  with  the  tools  available. 
Casing  finally  driven  to  33  ft.  at  about 
6:00  p.m. 

29  -35  ft.     rock  fill.  June  18,  6  p.m.,  well  40  ft.;  June 

20,  2. p.m.,  well  49  ft.  deep.  At  35  ft. 
struck  boulder,  casing  glanced  by  its  side. 

35  -  49  ft.    rock  fill.  Difficult  to  pump  material  out  of 

well. 

49  -  51  ft.    gravel,  said  and  some  wet  clay.  Boring  is 

getting  eesier. 

SI  -  58  ft.    June  21.  Rock  fill  and  clay.  At  58  ft. 

encountered  9"  of  solid  rock;  drilled 
through  it. 

59  -  62  ft.    June  22.  Rock  fill;  hole  62  ft.  at  5:40  p.m.; 

casing  et  61  ft.;  usually  1  to  2  ft.  behind 
hole.  At  8:30  a.m.  June  23,  hole  at  61  ft. 
Material  filled  in  1  ft.  over  night.  Y/ater 
at  8  inches  from  top. 

62  -  65. ft.    Rock  fill  and  clay.  June  23,  4:45  p.m.,  hole 

67.5  ft, ,  cesing  64  ft. 

65  -  68   ft.          Stiff  clay  with  some   sand  end  a  few  stones;   can 

hardly  bore   it  with  three  men.   Difficult  to 
get  material  up  after  boring.   Material 
squeezed  in  over  night   from  67.5  to  65  ft. 
June  24,  6  p.m.,  hole  70  ft.,   casing  68  ft. 

68  -  70  ft.  Yellow  clay  end  sand,  some  rock  »  disintegrated 

aautl  Btotio.   rt'ator  0  inches.  June  25,  8-  a.m. 
manorial  equoczc<l  in  ovor  night  to  68  ft.  ,. 

At  72.2  ft.  June  -2S,:  -lo*t  jEOgor  down  rail,  casing  68  ft. 

Fiahedout  auger  end  moved  to  v;ell  No.  21. 
Used  12.5  ft.   10"  ceding,   68  ft.   8"  casing. 
Took  6  cr.mplec.  Yfcter  level  8".   from  curf.ce 
of  ground  at  hole. 


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.ANALYSES  OF  SAMPLES 


Wet  Sample 

Dry  Sample        I 

Sample 

Depth 

Moisture 

Sand  and   , 

Clay  by 

Sand  and 

Clay  by 

No. 

ft. 

,  I 

gravel  %  1 

subtract  % 

gravel  % 

subtract  $> 

1556 

56 

18.5 

I 

i 
68.5 

13.0 

84.0 

16.0 

1560 

60 

17.2 

64.0 

18.8 

77.5 

22.5 

1561 

61 

15.4 

72.8 

11.8 

86.0 

14.0 

1565 

65 

22,4 

34.3 

43.3 

44.2 

55.8 

1568 

68 

16.7 

58.4 

24.9 

70.1 

29.9 

1572 

72 

18.1   . 

39.1 

42.8 

47.9 

52.1 

Consult  for  CalaM'eras  Dam  failure  Engineering  News-Record,  Vol.  80, 
pp.  631,  679,  6$2,  and  704;  Vol.  81,  p.  1158. 


It  is  sometimes  advisable  to  use  wooden  piles  for  the 
purpose  of  making  examinations  at  a  foundation  site.  As  many  piles  as  may  be 
considered  necessary  are  driven  to  refusal  or  as  nearly  as  that  can  be  determined, 
in  order  to  discover  at  what  depths  at  different  locations  in  the  foundation  bed 
underlying  rock  or  other  hard  stratum  lies.  Frequently  it  is  necessary  to  use 
shod  piles.  In  work  of  this  character,  wherever  possible,  the  pile  should  be 
pulled  so  that  the  depth  of  penetration  may  be  verified;  otherwise  it  is  question- 
able whether  the  pile  may  not  have  been  broken;  or  the  point  of  the  pile  may  have 
wandered.  A  misinterpretation  of  results  due  to  faulty  data  must  be  prevented. 

A  few  test  piles  may  be  driven  outside  the  proposed  foundation  plan  in 
order  to  determine  whet  depth  of  penetration  it  is  advisable  to  specify  for  the 
actual  foundation.  In  this  way  it  is  possible  to  r.void  specifying  or  ordering 
piles  of  greater  length  than  it  is  necessary  to  use.  Test  piles  also  are 
frequently  driven,  either  singly  or  in  groups,  and  are  then  heavily  loaded,  to 
determine  their  safe  bearing  po^or.  -:  For,  important  structures  this  is  a  necessary 
part  of  the  preliminary  work  as  it  determines  the  number  of  piles  required;  henca 
governs  very  largely  the  design  of  the  foundation;  and  may  have  considerable 
influence  on  the  typo  of  super-structure.  The  formulas  for  determining  bearing 
power  of  pilos  arc  doscribod  in  Chapter  VI. 


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EXAMPLES  OP  TEST  PILE  EXAMINATIONS 


Harbor  Development  at  South  San  Francisco. 

For  proposed  harbor  developments  in  San  Francisco  Bay  near  South  San 
Francisco,  it  became  necessary  to  study  the  bearing  power  of  the  bay  bottom  to 
determine  (1)  bulkhead  construction  (2)  capacity  of  the  soil  to  support  hydraulic 
fill  and  buildings,  and  (3)  ability  to  sustain  proposed  earth  jetties. 
Nine  test  holes  sunk  by  boring  gave  the  following  results :- 

TEST  HOLES 


No. 

Depth,  ft. 

Material 

1 

0-34 

soft  blue  mud  -  still  mud 

2 

0-34 

soft  blue  mud  -  still  mud 

3 

0-34 

soft  blue  mud  -  still  mud 

4 

0-62 

soft  blue  mud  -  drill  stuck 

at  62 

probably  sand 

5 

0-35 

soft  blue  mud  -  nearly  lost  drill,  1  ft.  in  send; 

very  fine,  packed 

at  35 

find  gray  sand 

6 

0-50 

soft  blue  mud 

at  50 

fine  gray  sand 

7 

0-35 

soft  blue  mud  -  still  mud 

8 

0-20 

soft  blue  mud 

20  -  20.5 

fine  green  sand 

20.5  -  25 

sand  and  mud 

25  -  30 

mud 

9 

0-17 

soft  blue  mud 

at  17 

fine  green  sand 

The  table  shows  that  with  few  exceptions  the  site  consists  of  soft  blue 
mud  for  depths  of  35  ft.  or  more.  The  ground  is  compressible,  both  for  the 
harbor  and  tide  lend  areas.  Under  loading  the  ground  flows  laterally,  indicating 
thet  supported  structures  should  be  of  light  weight.  For  instance,  earth  jetties 
would  be  more  permanent  if  stable,  but  the  lighter  weight  of  creosoted  pile  y 
jetties  caused  their  recommendation,  though  of  greater  cost  and  shorter  life. 
Bulkheads  for  piers,  wharves  and  retaining  dikes  were  designed  to  retain  earth, 
diminish  lateral  flow  of  mud  and  restrict  settlements. 

Eight  test  piles  were  driven.  The  hamaer  used  weighed  3200  Ib. ,  fe.lling 
from  10  to  20  ft.  The  total  pile  penetration,  excepting  pile  fco.  3,  was  large, 
being  58  ft.  or  more.  The  average  bearing  capacity  wes  not  high;  for  test  pile 


.       .    • 


.•:  -o-  cr;,-    re 


'  .••%££,«. 


v    -,rrf  ,    ;;+ 

;    -     /v:ij 


—  J-7".        -        -•.i 


/,         .^JL.'.:;    -    :j.  ;  •      -j.-/'J 

'-    -  -  :     -    ~    '.'  '-.   6.-;.:  !   j-i 


-  r'     •''  •"'•    '  "••   '•''  :  -   !«!.     e;,   •;'   &;  . 

--'       -'   "  ,    2f.  ;V      -  V;   V          • 


•~;       '^     ';.       •  C    ..f  ^ 

-.iLi::   -    jyr     j.  -..',:    t>;r 


er.  , 


;'  c    -    ' 

."-• 


— j.j!>X-  _-  .'_•:•  \;_  i-Li  i 


.-•  :",', 
x^-i-O       "  t  ^     -y 


d.'i:* 


J  i  ^=    .  -•„;  :  .i-     ^r     i.;fi    ,  -j._-    _:.        ;_,  ...,  , 

v-  ••  -  —fA.  -..  ,  ..'  ;. 


o^cs-i..lc    ,  Ww,-*s 


...  fe 


": 


Eo.  6  it  was  exceptionally  low. 

JBEAKING  PC77SEL  0?  r;'I 


PI^ES 


No.    j       Penetracion,    ft.                             Beaming  Pov/er, 

Tons 

1 

58.5 

12.7 

2 

61. 

11.7 

5 

37.6 

35.0 

4 

59, 

35.5 

5 

58. 

33.0 

6 

56.7 

3.5 

7 

60          '                                             15.0 

8 

75                                                       25,5 

As  examples  of  the  actual  field  data  the  fecords  for  tost  piles  I*os-  3 

I 

and  6  are  submitted: 

Examination  of  Site ,  South  San  Francisco  Harbor  Project 
Test  Pile  t.o.  5 

Nature  of  soil  -  soft  blue  niud  on  surface 
Condition  of  pile  -  sound 

length  =  61  ft.  8  in.       diam.  at  middle  =  10  in. 

diam.  at  butt  =  13  in.      difui.  et  point  =  8  in* 

Time  of  Test,  Feb.  2Q,  1912.   Began  driving  9:30  a.m.;  finished  driving 
10:30  a.m. 


Penetration,  ft. 

18.85 
20.75 
21.60 
22.40 
23.00 
23.75 
24.50 
25.25 
25.90 
26.60 
27.35 
28.10 
29.00 
29.85 
30,50 
31.35 
32.00 
32.70 
33.15 
33.60 
34.05 
34.95 
35.55 


Fall  of  H£.m.'.iera    ft. 


7. 

4 

to 

3.3 

9. 

3 

to 

10. 

1 

10. 

1 

to 

11. 

0 

11. 

0 

to 

11. 

5 

11. 

5 

to 

12. 

3 

12. 

3 

to 

13. 

0 

13. 

0 

to 

13. 

8 

13. 

8 

to 

14. 

4 

14. 

4 

to 

15. 

1 

15. 

1 

to 

15. 

9 

15. 

,9 

to 

16, 

6 

16. 

6 

to 

17, 

5 

17. 

5 

to 

18. 

4- 

18. 

4 

to 

19. 

1 

19. 

1 

to 

19. 

9 

19. 

9 

to 

20, 

5 

20. 

5 

to 

21. 

2 

21. 

2 

to 

21. 

7 

21. 

7 

to 

22. 

1 

22. 

1 

to 

22. 

0 

22.0 

to 

23. 

5 

18. 

5 

to 

IS. 

1 

19. 

1 

to 

19.3 

iio.    of  Blov/s 

4 

5 

5 

5 

5  or  6 

5 

5 

5 

5 

5 

5 

5 

5 

5 

5 

5 

5 

5 

5 

5 

5 

5 

5 


.       V  -. 


••'-£..- 


11 

Penetration.,  ft.        Fall  of  Hammer ,  ft .         Ho.  of  Blows 


35.75 

19.3 

to  19.7 

5 

36.20 

19.7 

to  19.9 

5 

36*40 

19.9 

to  20.1 

5 

36.60 

20.1 

to  20.8 

10 

37.30 

20.8 

to  21.1 

5 

^7  fiO 

Kote:  Stopped  driving  because  the  pile  point  appeared  to  be  splintering 
ind  brooming. 

Fall  of  tide  during  driving  about  1  ft. 


Test  Pile  Ho.  6. 

Nature  of  soil  -  soft  blue  mud. 
Condition  of  pile  -  sound 

length  of  pile  =63  ft.  0  in.       die.ni.  at  middle  =  10  in. 

diam.  at  butt  =  12  in.  die.ra.  at  point  -  7.6  in- 

Time  of  Test  -  Feb.  27,  1912.   Began  driving  at  8:00  a.m.;  finished 
driving  at  8:45  a.m. 

Penetration,  ft.  Fall  of  Hamaer.  ft.   Mo.  of  Blows 

29.4  9.6  to  25.3             5 

45.1  20.7  to  32.3 

56.7  19.7  to  24.0 
61.0 

At  penetration  61. o  a  puach  wes  put  on  but  was  not  successful  ss  driver  was 
not  prepared. 

63.8  14.2  to  17.0 


Bearing  Po-.ver  Computations 
To  compute  bec.ring  pover,  Engineer  ing  l\ie\vs  formula  vc.s  uced,   see  Chr.p.  VI, 

equation  5. 

r  =  1.8  tfh 


3     +    1 

r  =  pile  resistance   in  Ibs.,  \7  =  hc.mmer  v«eight   in  Ibs.,   h  -  hr.nmer  fall   in  ft., 
a  =  pile  penetr:  tion  in  inches.   The  coefficient  2   in  the  usual  formula  is  replr. 
by  1.8  on  the  resumption  thc.t  ten  per  cent  of  the  hrmmer  fell  ia  lost  in  friction 
civl  from  other  causes. 

For  pile  Mo.   3,   s   for  the  Ir.st  5  blo-./s  is  one-fifth  of  37.6  -  37.3  =  0.3 
ft.,    or  0.72   inches;  V/  =  3200  lb.,   h  -  20.95  ft.;   hence  r   =  70  •'         ^b,    or  35  tons 


•*-  v         .-,-. ........  ,*  r  ,  ' 

«wi      »   Jt3.  j.iZii,         -     --*:_-.  •. 


0   "••;    oo      T-C. 
j  ,OS   o:r      y    /f 
8,  OS    C'       -  ,  ,. 
•.,0i; 


o,  ,r. 


AX'..    ••...:     '  i  :,.    -    _*:   •    i-^    .  :  : 

T.Vv,    '     -     vii."  :"•'  i?i_'- X  J 


i.  C.U.    io     -  0': 


c  -civ  c: 
C  -.,.   id 


•t-         •  .->-;  -^  -  -  to.-.  - 

•-  .t        .  -  ,  *;  .t  -'    ~   i  Y  r-;r  -j-^u-i:_; 


C.V1    ; 


1-   .. 


:;j      .i,       •       ./..    .     J.    ~     Ci 

^ay  erfj   - 


12. 
with  a  safety  fcctor  of  6.  For  pile  No.  6,  r  =  6900  Ib. ,  at  56.7  ft.  penetration. 

In  studying  the  above  field  reoorde  it.  is  to  be  note:  that  pile  Ho.  6 
represents  the  worst  cc.se  ant!  pile  No.  3  one  of  the  more  favorable  cases  of  bear- 
ing capacity  on  a  treacherous  foundation  site.  Some  of  these  piles  sanfc  under 
their  own  weight  an-",  the  dead  weight  of  the  hammer  from  10  to  20  ft.  or  more 
and  also  in  the  progress  of  driving.  For  instance,  pile  Ko.  6  penetrated  from 
29.4  to  45.1  ft.  in  5  blows;  an  average  of  about  3.1  ft.  per  blow.  At  a  depth  of 
62  ft.  the  same  pile,  urT.er  a  hrmmer  fall  of  15  ft,,  in  the  finr.l  five  blows,  was 
driven  2.8  ft.,  an  average  of  0.56  ft.  per  blow.  On  the  other  hand  in  the  begin- 
ning of  .driving  pile  No.  3  in  four  blows  penetrated  from  18.85  to  20.75  ft.,  an 
average  of  0.5  ft.  per  blow.  Pile  No.  3,  under  a  hammer  fall  of  21  ft.  recorded 
a  penetration  of  0.3  ft.  from  the  last  five  blows,  or  an  average  of  0.06  ft, 
per  blow. 

Auditorium  Building,  Oakland,  California 

As  another  example  of  foundation  examination  bj  test  piles,  reference  is 
made  to  the  Auditorium  Building,  Oakland,  California,  which  structure  rests  on 
filled  ground  south  of  Lake  Merritt.  Fig.  40  shows  the  location  of  six  test  piles 
in  an  area  186  ft.  x  400  ft.  The  field  recor-'  for  only  one  of  these  piles  is 

given  below. 

Test  Pile,  Ho. 6. 

Date  -  July  22,  1912  butt  end  =  14.5  in. 

Dimensions  -  tip  end  =  8  in,  length  =  72  ft.  9  in. 

Mo.  of  Blows   Drop  of  Hammer  Distance  ,  Total  Penetration   i   Remarks 


21 

5  ft. 

:  23' 

0"   I 

23' 

0"            soft 

•7 

5 

i  6 

o   \ 

29 

0 

15 

10 

•  11 

0 

40 

0 

18 

12 

11 

0    i 

51 

0       '  hard  mrterial 

16 

12 

3 

6 

54 

6 

17 

14 

2 

2 

56 

8 

10 

20 

1 

5 

58 

1 

10 

20  • 

1 

4 

59 

5 

Stjopped  driving;  pile  went  down  1.6  in.  for  the  last  blow;  pile  started  to 
split.   Berring  value 

r  =  2  x  2550  x  20  =  19.5  tons- 
2.6  x  2000 


..;••  . 

• '- r      •• 


•.«•-.-, 


.-I    c-    - 


-  0-    :^C  0 


'  ' 


:         .- 


.     .     •  .      ;         •; 


r  -  -• 

A  *•    x.' 

?  — 

"civ;  .  ?"£"-« 


13. 
No  reduction  was  here  made  for  loss  of  energy  in  the  drop  h. 

This  steel  frr.med,  concrete  and  masonry  building  has  its  structural 
columns  supported  upon  reinforced  concrete  footings  which  in  turn  act  c.s  grillage 
cr.ps  to  clusters  of  piles  driven  to  depths  of  from  60  to  75  ft. 

Test  Piles  ot^  Cqlaverr s  Dam. 

Eighty-four  piles  v.ere  driven  in  r.  centre  1  pool  of  clay.  From  these 
records  end  the  logs  of  r.  number  of  v/ells  estimates  v;ere  male  for  the  quantities 
rnd  locations  of  material  o£  Different  grades  of  solidity.  The  field,  notes  for 
one  of  these  piles  is  submitted. 

Test  Pile  l<o.  82. 

Location  XXXVIII  +29;  27  +  35.  East  line.  Elevation  of  ground  658  ft. 
Pile  dimensions:  V/eight  of  pile  =  1420  *  100  Ib. 

length  =  41.83  ft. 

butt  circumference  =  3.38  ft. 

middle  circumference  =  3.00  ft. 

point  circumference  =  2.58  ft. 
Nature  of  ground  =  soft,  wet  surface  of  submerged  portion  of  clay  pool 

in  dam. 

Penetration  due  to  ov/n  v/eight  =  9.0  ft, 
Penetration  due  to  hr inner  v/eight  =  7.5  ft. 
Total  stc.tic  penetrrtion  =  16.5  ft. 

Driving  Log 


.  B10\7 

i\o. 

iDrop:.  of 
''hammer,  ft. 

Pen.  Pile    TOLal 
per  blov;  ft.  pen.  ft. 

Avg,  of  5  blov/s     Elev. 

Re  narks 

'.rop  ham.   Pen,  of   of  pt, 
ft,      pile,  ft  of 
pile 

static 

16.5 

642 

Date 

:. 

3.0 

1.2 

July  22. 

2 

15.8 

2.8 

1918; 

0 

:  14.0 

1.7 

i 

time  of 

4 

16.5 

1.6 

start 

5 

15  .  3 

1.5         25.5 

12.9        1.8    632 

10:25 

5 

.  17.6 

l.G 

a  .  m  . 

7 

16.1 

1.4 

8 

16.6 

1.1                   j 

c 

17.4 

1.2 

1C 

17.8 

1.3          32.1        17.1        1.3    G26 

11 

-  18.3 

1.3 

12 

18.5 

0.5 

13 

.  19.0 

0,6 

14 

:  19.0 

0.4 

15 

'  19.8 

0.7         35.6 

18.9        0.7    623 

-  '          : 


•  -   ;  --  - 
'*•:     "  '  ' 


:0::   a  « 


•i  •  •:  .v".-:i 


.v   ^ 


'-•'"    '• 


,;j  ,v--I_    - 
•      re    •.-.V.- 


'•.v*  j^-- 


.-__  . 

t       .;   -C     Ovf  .:> 


. ..  ' 


Driving  Log  Test  Pile  Ho. 82,   continue-:1. 


14 


J  Blow 

rDrop  of 

jPen.  pile  j  Total  pen-r 

Averr.ge  of  5  blows 

Elev. 

fiemarks 

}  No. 

.hammer,ft. 

;  per  blow  :     etrr.tion 

rlrop  ham-     pen.    of  ; 

of 

\ 

i 

ft.                    ft. 

mer,   ft.         pile,  ft* 

pt. 

j 

of 

• 

. 

I 

i 

pile  . 

:  16 

18.8 

0.4 

!   IV 

19.0 

0.6 

i 

i 

18 

18.9 

O.G 

> 

i 

19 

17.2 

1.1 

t 
j 

s 

20 

16,5 

0.9                   39.2 

14.1                     0.7 

619  '. 

Time  of  enc. 

:   21 

18.0 

0.9 

1 

10:33  a.m. 

:     22 

8.3 

0.4                  40.5 

15.8                    0.78*  j 

618  ! 

Sticking 

! 

out  1.5   ft. 

1 

i 

i 

*Avg.of 

j 

| 

last  5 

bl  ov;s  . 

Berring  power  of  pile  =     1.8  x  2500  x  15.8  =  3.4  tons 

(9.36+1)   2000 


5-  Borings  \7ith  the  Sand-Pomp.  Sand,  when  dry  or  compact,  is  one  of  the 
most  difficult  materials  to  penetrate.  It  is  readily  traversed  when  wet.  The 
sand  pump  (see  Fig.  3)  is  a  hollow  cylinder  1  -  6  ft.  in  length  r.nd  3  -  8  or  10 
inches  in  diameter,  fitted  with  a  simple  flap  valve  at  the  bottom,  opening  in- 
ward; the  whole  suspended  from  a  stout  rope  or  wire,  or  coupled  to  rods  or  pipes. 
The  sand  pump  is  lowered  into  s.  hole,  the  latter  containing  v/ater  at  the  bottom. 
The  pump  is  churned  rapidly  up  and  down  by  hand  until  it  partially  or  wholly 
fills  with  mud  or  sand  and  water.  It  is  then  drawn  to  the  top  where  the  collected 
material  is  examined  rnd  emptied.  The  method  determines  the  material  passed 
through  but  does  not  exhibit  it  in  its  natural  condition.  For  exrmple,  stiff  clay 
is  churned  into  soft  pasty  mud.  The  condition  of  the  .material ,  especially  its 
compactness,  may  be  inferred  however  by  an  experienced  operator  from  the  diffi •*.'-. 
culty  and  rate  in  sinking  a  test  hole. 

Quicksand,  the  most  troublesome  of  all  foundation  materials,  is  composed 
of  excessively  round  sand  grains  mixed  with  water.  If  this  material,  in  its 
native  condition,  be  found  held  between  layers  of  clay,  it  may  easily  be  taken 
for  compact  sand,  giving  no  intimrtion  of  its  dangerous  character.  Fine  sand  shouln 


•  .?.-•• 


-,-VC-LJ 


-j-oo    K?   ,  ''.'tv/  t 


- 


r,    -..;j  i  :;  ijr  R      .  •..  -7  .'.'••,     ^ri-    '•:    VJ 
-*          •  .' 


..•>-:--..•  ;.noo  ci    .  -;  r 


II.: 


:— »  .,'f  --t  ? 


•   J;    .  ..'-£.0   ". 


15 

be  very  closely  examined  with  a  microscope.  A  solid  core,  showing  the  actual 
condition  of  the  material  in  place  at  any  depth  desired  may  be  obtained  by 
driving  down  a  smaller  open  ended  pipe  to  the  bottom  of  the  hole  excavated  by  the 
snnd  pump.  It  is  sometimes  necessary  to  use  a  vacuum  pump  to  keep  and  lift  the 
.material  in  this  drive  pipe.  If  the  material  is  soft,  the  hole  must  be  cased 
with  iron  or  terra  cotta  pipe,  which  usually  will  have  to  be  driven  by  hammering 
with  a  heavy  wooden  maul,  a  lever  press,  or  a  light  improvised  pile  driver,  the 
material  being  simultaneously  excavated  from  the  inside  of  the  casing,  and  a 
little  in  advance  of  its  botto  m,  with  the  sand  pump.  The  apparatus  will  not  pen- 
etrate gravel  and  goes  very  slowly  in  compact  or  indurr.ted  clay.  It  gives  the 
best  results  in  comparatively  loose  soils  using  light  casing.  It  is  ersily 
stopped  by  boulders,  logs,  roots  or  other  obstructions. 

Sand-Pump  Borings 
Civic  Center,  San  Francisco 

The  Civic  Center,  Van  Ness  Ave.  and  Market  St.,  San  Francisco,  presents 
a  foundation  site  in  what  was  once  swamp.  The  ground  water  level  is  within  10  ft. 
from  the  surface.  For  depths  of  100  ft.  or  more  borings  encounter  sr.nd  r.nd  clay 
in  lasers  with  numerous  thin  seams  of  peat  or  soft  vegetable  earth.  The  site  is 
compressible.  The  City  Hall  and  Auditorium  buildings  rest  on  reinforced  concrete 
footings  with  a  soil  pressure  of  2,5  to  3.0  tons  per  sq.  ft.,  figuring  dead  load 
and  10  Ibs.  per  sq.  ft.  live  load  on  each  floor.  Figs.  4D  f.nd  4E  show  ten  borings 
for  the  City  Hall  and  eleven  for  the  Auditorium  building;  also  typical  profile 
foundation  sections  assembled  from  the  boring  records.  As  examples  of  the  field 
notes  the  logs  are  submitted  for  hole  No.  6,  City  Hall  site,  and  No.  1,  Auditorium 
site. 

Record  _of_  Boring,  City  Hall  Site,  San  Francisco 
Hole  Ho.  6,  October  30,  1912  4  elevation  top  of  hole  =  51.51  ft. 

Depth.                Ijatnre  of  Soil  Jar  No . 

12 '6"  dry  yellow  sand  1 

12  6  water 

19'  yellowish  wet  sand  2 


.  J..ii*3';  3;i*  3fi  jr.xrf  a   ,  O»IGC,  in/tja  A   .:  •  cd 

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-  .?*  -WlijT-  0-' 

•Ji&  :••  -,j   c;nk.r  Vj;;,-:  •  •  .:•  --;;j  c?  -^-.-.aoov-      :  .-.        .      ^t   rl     <•$£... 

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16. 

Depth  Nature  of  Soil  jar  Ko. 

19'  6"           decomposed  vegetable  substance,  hard  2 

25'              yellowish  wet  sand  3 

47'              grayish  wet  sand  4 

47'  6"           decomposed  vegetable  substance,  hard  5 

78'              fine  grayish  wet  sr.nd  6 
78'  1"           1-in.  strata  decomposed  vegetable  substance, hard   7 

fine  grayish  wet  sand  8 

80*              encountered  firm  blue  clay  9 

104'             tough  blue  clay  9 

108'             tough  yellow  clay  10 

109'             soft  yellow  clay  and  sand  11 

coarse  sand,  yellow  clay  12 

coarse  sand,  and  yellow  clay  12 

122'             hard  sr.ndy  yellow  clay  13 

Record  of  Boring,  Auditorium  SiteA  San  Francisco 
\7ell  Ko.  1,  Jan.  1913,  elevation  to?  of  hole  -  +47.60  ft. 

2'  0"  fill 

2'  6"  soil 

18'  4"  yellow  sand  (dry)  1 

gray  s  and  (wet  J  2 

67'  11"  green  sand  (v/et )  3 

68'  1"  soft  vegetable  errth  4 

70'  9"  green  sand  (wet)  3 

71'  9"  vegetable  earth  5 

73'  9"  green  clay  6 

80'  0"  hard  sandy  clay  7 

81*  0"  hard  green  clay  8 

92'  8"  green  sand  (hard)  9 

These  borings  were  all  mrde  with  a  hand  power  apparatus.  The  6-in. 
casing  was  sunk  under  pressure  from  a  wooden  lever .  The  boring  tool  or  plunger 
was  operated  by  using  a  small  derrick  similar  to  ffig.  2,  to  which  a  windlass  was 
attached.  At  intervals  the  .naterial  was  lifted  with  a  sand  pump;  sonples  being 
taken  as  above  indicated. 

In  some  holes  in  hard  ground,  as  those  at  Bcalt  Hall  and  the  Agriculture 
Building,  cited  under  heading  No.  7,  it  was  necessary  to  supply  water  from  time 
to  time  to  ease  sinking.  At  the  City  Hall  and  Auditorium  sites  the  ground  water 
and  loose  soils  made  this  unnecessary. 

6*  Sinking  with  V/'ater-Jet.   In  this  method  a  pipe  2.5  to  6  in.  diameter 
is  driven  into  the  soil  r.nd  a  smaller  pipe  inserted  inside,  through  which  vr.ter 
is  forced  under  pressure. 


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17. 

Plant  required  consists  of  two  sizes  of  screw  pipe,  cut  to  convenient 
lengths  of  6  to  20  ft.,  and  threaded  at  "both  ends,  a  simple  frame  or  derrick  10 
to  20  ft.  high,  fitted  with  block  and  tackle,  or  winch,  to  enable  a  100  to  200 
Ib.  weight  to  b  e  raised  a  few  feot.  v.^tically  and  dropped;  a  force  pump,  usually 
worked  by  hand,  with  heavy  rubber  hose  connections.  The  procedure  is  as  follows: - 
the  outer  larger  pipe  is  driven  into  the  ground  a  few  feet  by  dropping  the  weight 
on  a  cap  temporarily  screwed  to  its  top.  The  smaller  or  v\e.sh  pipe  is  then  inserted 
and  water  forced  downward  through  it  under  pressure  flowing  up  in  the  annular 
space  between  the  pipes,  bringing  to  the  surface  dislodged  mud,  sand  and  pebbles 
where  they  maybe  caught  in  a  bucket  and  exan  ined  after  settling- 

If  it  is  desired,  to  examine  material  in  the  condition  in  which  it  is 
found,  drive  down  an  open  ended  pipe  a  foot  or  two  and  pull  up  a  cylinder  of 
clay  or  sand.  Vacuum  is  sometimes  used  to  retain  the  specimen  cylinder  of 
material  in  the  inside  of  the  drive  pipe. 

Hydraulic  or  inside  couplings  should  be  used  if  much  driving  is  to  be 
done.  If  the  soil  is  reasonably  firm  the  wash  pipe  may  be  dispensed  with  and 
one  pipe  connected  directly  to  the  force  pump,  the  vr.ter  and  loosened  material 
rising  to  the  surface  in  an  annular  spree  which  is  formed  around  the  pipe. The 
pipe  i:T.y  sink  of  its  own  weight,  or  it  mr.y  be  necessary  to  alternately  raise 
and  lower  it  and  perhaps  rotate  it  to  secure  the  best  reailts.  The  pump  should 
be  worked  continuously  as  the  soil  is  apt  to  settle  comprctly  r round  the  pipe 
if  the  sinking  is  stopped*  even  for  a  few  minutes.  This  method  is  probably  more 
rapid  and  economical  where  it  C'nbe  used,  than  rny  other,  A  derrick  is  un- 
necessary, though  it  is  advisable,  if  depths  grerter  than  30  to  40  ft.  are  to 
be  reached,  in  order  to  permit  the  use  of  long  lengths  of  pipe.  Fig.  4  (Engineer- 
ing iiews,  Vol.  21,  p.  423)shows  a  simple  frame  suitable  for  this  work  or  for  a 
sand  pump, 


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13. 

7.  Drilling  with  Artesian  V/ell  Boring  Tools.  For  a  complete  discussion 
this  subject  in  itself  would  require  an  extensive  description.  It  cr.n  only  be 
mentioned  briefly  here.  It  is  employed  for  special  cases  of  deep  or  difficult 
foundation  tests  where  simpler  methods  are  deemed  insufficient.  The  apparatus 
consists  principally  of  heavy  steel  drills,  suspended  by  steel  cables  or'  ropes 
and  raised  and  lowered  rapidly  by  hoisting  engines,  together  with  a  special  form 
of  pile  driver  for  driving  iron  or  steel  casing.  Large  numbers  of  other  tools  are 
used  for  special  purposes  or  particular  formation;  such  as  sand,  pumps,  ehisel 
bits,  augers.  Holes  can  be  drilled  through  any  formation  except  the  hardest  rock 
and  to  depths  of  3000  ft.  or  more.  The  casing  is  usually  from  4  to  18  ins.  in 
diameter.  The  reader  is  referred  to  descriptions  of  apparrtus  for  s inking 
'artesian  wells  for  mter,  oil  or  gas;  he  should  also  consult  the  trade  literature 

for  artesianwell  boring  tools.  Cf.  V/ater  Supply  Paper  No.  257,  U.S.G.S.  ;  a 

ty 
descriptive  and  excellent-/ illustrated  article  on  "V/ell  Drilling  Methods"  by  I. 

Bowman.  This  paper  describes  the  diamond  drill  also. 

Sinoe  these  tools  may  sink  wells  readily  to  3000  ft.  and  more,  the 
usual  foundation  examination  offers  a  simple  application  because  the  depths 
required  for  foundation  explorations  rarely  exceed  100  to  200  ft.  In  ordinary  soil 
formations  it  is  commonly  possible  to  dispense  with  any  driving  apparatus  and  to 
sink  the  casing  by  weighting  it  while  it  isb  eing  worked  back  and  forth  with 
plenty  of  water  to  decrease  the  friction  of  earth  on  its  sides.  A  simple  lever  is 
frequently  used  to  force  the  casing  down  by  loading  its  outer  end  with  bags  of 
sand.  The  casing  may  be  heavy  screw  pipe,  mr.de  of  steel  or  cast  iron.  If  inside 
couplings  are  used,  there  is  less  friction  on  the  sides.  The  "stove  pipe"  casing 
more  commonly  used  consists  of  two  concentric  cylinders  of  sheet  iron  or  steel, 
one  of  them  fitting  closely  inside  the  other.  These  are  lap  riveted  or  welded 
in  common  lengths  of  2  to  3  ft,,  frequently  being  made  from  sheet  iron  or  steel 
at  the  site  of  the  work.  The  casing  is  formed  in  place  so  that  the  inner  and  outer 

casings  break  joints,  forming  a  continuous  column  stiff  enough  for  ordinary 
purpose So 


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19. 

Boalt  Hall ,  Universi  ty  _of  California 

Fig.  4F  indicates  four  borings  sunk  in  1909  on  the  site  of  Boalt  Hr.ll, 
University  of  California,  using  machine  power  well  tools  for  6-in.  holes.  For 
part  of  the  depth  it  vr.s  necessary  to  sink  casings.  At  intervals  the  material  was 
taken  out  with  a  large  sand  pump, 

Agriculture  Hall,  University  ojf  California 

Borings  of  similar  nature  were  nade  in  1910  for  the  Agriculture  Bldg. , 
University  of  California.  In  this  case  one  hole  was  driven  42  ft.  to  test  the 
nature  of  the  foundation  soil  which  was  gravelly  clay  for  the  entire  depth.  The 
three  other  holes  were  stopped  at  much  smaller  depths.  In  every  case  the  top 
soil  was  adobe;  the  gravelly  clay,  yellow,  and  identical  with  that  found  at 
Boalt  Hall. 

Calaveras  Dam 

In  July  1918  about  25  wells  were  sunk  by  power  rigs.  The  following  is  the 
record  of  a  well  driven  in  the  center  or  core  of  the  dam. 
Well  No._23_;  Drilling  Log;  Power  Big  A. 

Location  XXXIV  +  00       Elevation  661.3  (referred  to  water  surface; 
22  +  21  ground  0.1'  lower  at  well) 

July  1,  1918,  started  drilling  at  4:50  p.m. 

0»-  8.5  ft.       liquid  clay,  very  wet  and  muddy  due  to  nearby  excavation 

and  water  submergence 
8.5  to  14  ft.       rock  fill;  this  material  will-not  stand  up;  caves  in 

readily, 
Hole  14  ft.  Casing  14  ft   Uater  at  ground  surfrce. 

July  2,  1918. 

14  to  51  ft.       rock  fill;  ;nr.teiir.le  aves  in  re.-dily,  but  stands  better 

than  that  between  8.5  and.  14  ft.  Casing  hrd  to  be  kept 

close  down. 
51  to  57  ft.       rock  fill  with  some  soft  clay.  Y/ill  not  stand  up.  Took 

a  sample  at  57  ft.  Material  flows  into  casing. 
57  to  60  ft.        clay,  rather  stiff;  sample  at  59  ft.  This  clay  is  of 

medium  stiffness. 

Hole  60  ft.  Casing  60  ft.  ":Jater  at  surface  of  ground. 
July  3,  1918. 

60  to  68  ft.       sluiced  shale  and  clay.  Took  samples  at  66  ft. 

68  to  74  ft.       sluiced  shale  with  very  little  clay,  will  not  str.nd  alone.. 


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20. 

stiff; 
74  to  77  ft.  clay  with  a  little  gravel;*  Took  sanples  at  557  ft. 

\7ater  8  inches  r.bove  ground  at  12:00  M. 
77  to  80  ft.  clay;   squeezed  into  hole;   rather   stiff;  sample  at   79   ft. 

July  8,  1918. 

80  to  84  ft.   clay;  very  stiff;  pure  clay 

84  to  87  ft.   clay  rnd  some  gravel;  took  a  sample  at  85  ft. 

87  to  88  ft.   11:00  a.m.  gravel,  boulders  rnd  some  clay.  Could  not  get 

sample,  struck  a  boulder  with  auger.  T/ater  1  ft.  rbove 
ground., 

Stopped  drilling.  Hole  88  ft.  Casing  85  ft.  85  ft.  of  8"  casing  used; 
6  srmples  taken. 

Analyses  of  Samples 


Sample 

Depth 

Viet  Samples 

Dry  Samples 

ft. 

Momsture 

Sand  & 

Clay  by  sub- 

Sand and 

Clay  by 

% 

gravel  % 

traction  % 

gravel  % 

subtraction  % 

2357 

57 

2  1.5 

22.3 

56.2 

28.4 

71.6 

2359 

59 

81.8 

21.0 

57.2 

26.8 

73.2 

2366 

66 

18.9 

40.5 

40.6 

50.5 

49.5 

2377 

77 

24.2 

12.1 

63.7 

15.9 

84.1 

2379 

79 

25.5 

9.7 

64.8 

13.0 

87.0 

2385 

85 

25.7 

5.4 

68,9 

7.3 

92.7 

July  10,  1918,  Perforated  casing  at  levels  10,  20,  30,  40,  50,  60,  70  and 

30  ft.  below  ground  surface 

July  17,1918,  water  level  0.2  ft.  belov/  ground  surface  =  elev.  661.1 
July  24,  1918,V/ater  level  0.0  ft. 

At  intervals  the  well  drill  was  removed  and  the  hole  cleaned  by  sand 
pump.  Then  samples  were  taken  by  letting  down  a  steel  auger.  Later  the  crsing  vr.s 
perforated  to  study  seepage.  Thewellwrs  pumped  and  allowed  to  fill  agrin.  These 
records  determined  the  degree  of  porosity  of  .irterials  in  different  parts  of  the 
dam. 

8.  Drilling  with  the  Diamond  Metal  _or_  Shot  Drills.  The  diamond  drill 
ie  an  expensive  apparatus,  used  chiefly  in  mining  and  tunnel  operations  to  drill 
through  solid  rock.  It  is  used  for  foundation  tests, only  in  connection  with  other 
methods  to  distinguish  with  certainty  between  solid  rodk  and  thin  Ir.yers  of  rock 
or  boulders.  It  is  required  for  important  structures  such  as  iiarine  foundrtions 
for  lighthouses,  for  bridge  piers,  dams  and  tunnels,  where  it  is  essential  thrt 
a  good  rock  foundation  be  secured. 


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21. 

A  diamond  drill  is  a  heavy  steel  cylinder  3  or  4  ins.  in  diameter  nnd 
about  1/2  in.  thick,  with  black  diamonds  or  other  very  hr.rd  substances  imbedded 
in^Lts  lower  toothed  end  (see  Fig.  5).  It  is  rapidly  revolved  and  cuts  out  a 
solid  core  which  maybe  broken  off  from  time  to  time,  caught  by  special  tools 
and  brought  through  the  hollow  stem  to  the  surface.  Sometimes  hardened  steel 
tools  without  diamonds  are  used,  or  hollow  drill  rod  apparatus  with  a  combination 
of  vertical  churning  and  rotating  motions. 

Core  rotary  drilling  apparatus  with  steel  shot  instead  of  diamonds  is 
now  common  practice.  Because  of  the  continually  increcsing  cost  of  black  carbons 
or  diamonds,  at  first  steel  cutters  were  introduced,  of  many  forms  of  cutter,  but 
found  inexpedient  except  for  the  softest  shales.  Stone  sawyers  were  the  first  to 
study  substitutes  for  sand  in  sawing  stone  and  finally  introduced  the  use  of 
chilled  steel  shot  of  varying  size,  according  to  the  work' to  be  done.  These  shot 
were  found  to  but  the  rock  very  fast  and  at  smaller  cost,  and  as  the  rock 
increased  in  hardness  their  efficiency  increased.  It  v/as  but  a  step  to  the  use  of 
steel  shot  under  circular  hollow  bits  for  cutting  a  core.  Consult  trade  catalogues 

Q-eneral  Precautions  for  lest  Borings, 

Erroneous  impressions  may  be  received  when  the  lower  end  of  a  pipe  or 
rod  is  deflected  from  its  course  or  stopped  by  boulders.  Boulders  are  frequently 
removed  or  broken  up  by  small  charges  of  dynamite  dropped  into  the  hole.  The 
outside  or  inside  pipe,  auger,  casing  or  sand  pump  may  be  easily  stopped  by 
boulders,  large  roots  and  buried  logs.  Pipes  may  be  clogged  at  any  moment  by  small 
stones  or  gravel  and  the  consequent  sinking  conditions  thus  mry  give  the 
impression  of  too  firm  a  material. 

It  is  difficult  to  use  any  methods  of  test  boring  in  compact  sand  or 
gravel,  and  then  only  in  the  presence  of  plenty  of  water.  Uater  nr.kes  it  difficult 
to  judge  the  character  of  the  sand  in  place,  especially  of  its  comprctness.  Any 
method  of  test  boring  which  uses  a  considerable  quantity  of  water,  such  as  the 
Y/ash  Drill,  -Sand  P^mp..  or  \7ell  Boring  Tools,  makes  it  uncertain  to  judge  of  the 


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character  of  the  material  in  place.  It  is  advisable  in  such  cr.sos  to  frequently 
bring  up  samples  dry  by  the  use  of  special  apparatus.  This  is  difficult  and  some- 
times  impcs  sible  in  sand  or  gravel,  or  in  mixed  gravel  and  clay  or  indurated  clr.y, 

A  c'onsiderable  number  of  borings  should  be  mr.de  and  if  results  apperr 
erratic  the  examination  should  be  continued.  For  importrnt  foundations  on  solid 
rock, borings  should  enter  into  the  rock  for  several  feet  by  employing  the  diamond 
drill  or  heavy  well  boring  tools,  otherwise  the  facts  crnnot  be  accepted  with 
confidence.  In  every  case  careful  and  complete  records  of  the  material  passed 
through  should  be  kept.  Test  borings  should  be  located  by  surveying.  A  special 
form  of  field  notes  for  keeping  a  log  of  borings  should  be  prepared  and  used. 
Examples  of  forms  have  already  been  given  in  what  precedes.  On  large  work  involv- 
ing many  borings,  a  printed  field  form  should  be  adopted  for  ready  reports  to 
be  made  by  the  foreman.  Consult  an  article  by  Smile  Low,  "Cost  of  \7ash  Drill 
Borings  in  Kew  York  State  Barge  Canal";  on  Deep  Y/aterways  Surveys,  1897-1900; 
Eng.  Hews,  Vol.  57,  1907,  p.  54.   If  sufficient  borings  are  made,  a  contour  map 
can  be  drawn  showing  subsurface  conditions,  the  arrangement  and  extent  of  strata 
and  the  position  of  solid  rock.  Profiles  or  cross -sections  of  river  channels  and 
bays  or  swamps  are  frequently  made  from  records  of  test  borings.  Sometimes  samples 
of  material  are  kept  in  glass  tubes  or  bottles  with  the  layers  of  material  in 
regular  order.  Mrps  may  be  drawn  to  show  columns  of  strrta  in  the  positions  of  the 
borings,  the  conventional  signs  and  printed  .natter  depicting  clearly  the  nature 
of  the  ground,  All  methods,  except  "drilling  with  heavy  well  tooring  tools,  offer 
difficulties  when  working  in  grrvel  or  compact  sand.  The  number  and  location  of 
test  borings  depend  entirely  on  the  magnitude  of  the  particular  work  in  hand.  The 
engineer  should  be  guided  by  the  importance  of  the  structure,  by  the  uniform  or 
non-uniform  character  of  the  test  results  and  by  the  characteristics  of  the 
formation  examined.  A  study  of  the  local  geology  is  frequently  a  great  help. 


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22 

Sub-Aqueous  Borings 

It  is  frequently  necessr.ry  to  make  borings  of  the  chr.rr.cter  already 
described  in  ground  under  water.  In  such  cases  the  boring  outfit  is  placed  upon 
a  scow  or  barge.  In  mrjiy  instances  in  deep.vvr.ter  or  in  swift  tides  or  currents, 
or  where  the  water  may  be  rough,  it  is  necessary  to  use  a  power  pump  for  forcing 
water  through  the  small  pipe.  These  examinations,  as  well  as  borings  into  rock  by 
diamond  drill  or  other  processes,  mr.y  be  successfully  executed  in  swift  currents 
and  even  in  the  open  ocean.  They  have  been  made  in  connection  with  examinations 
for  harbor  improvements;  in  the  rr.pid  tidal  currents  of  the  East  River,  New  York 
City,  for  bridge  pier  sites;  along  both  the  Atlantic  and  Pacific  Coasts  of  the 
United  States;  and  in  similar  foreign  loortione.  If  the  water  is  quiet,  as  in  the 
slips  between  docks  and  piers,  a  sar.ll  scow,  15  by  20  ft.  plan,  with  a  well  in  its 
center,  and  fitted  with  a  hand  pump  will  be  found  satisfactory  for  ordinary  cases. 
V/hen  the  water  is  likely  to  be  rough,  or  where  the  currents  are  strong,  it  will 
be  necessary  to  make  use  of  a  larger  sew/,  strongly  built  and  fitted  with  a  pov/er 
pump.  A  pile  driver  scow  is  a  very  good  vessel  for  the  purpose.  The  regular  pile 
driving  leads  are  not  required  although  they  may  be  used  if  they  are  in  place.  A 
much  smaller  but  similar  frrme,  not  more  than  15  or  20  ft.  high,  is  ample  for  the 
purpose.  If  the  water  is  deep,  necessitating  considerable  length  of  pipe,  it  is 
advisable  to  use  the  pile  driver  or  hoisting  engine  for  handling  the  pipe, 
although  a  winch  worked  by  hand  is  usually  sufficient. 

The  scow  40  or  50  ft.  long  and  20  to  25  ft.  wide,  fitted  with  suitable 
appliances  already  indicated,  is  towed  to  the  position  where  the  eicaminations  are 
to  be  made.  If  the  current  is  always  in  one  direction,  as  in  a  river,  it  will 
only  be  necessary  to  anchor  the  scow  from  one  direction,  a.s  shown  in  Fig.  6, 
If,  ho- ever,  the  work  is  done  in  a  tidal  current  likely  to  run  in  both  directions 
before  the  position  of  the  scow  is  changed,  it  becomes  necessary  to  anchor  from 
both  directions.  The  lines  running  from  the  scow  to  the  anchors  should  have 
considerable  inclination  to  the  axis  of  the  scow,  so  that  it  vja.y  have  the 


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24 

.requisite  lateral  stability  of  position.  The  anchors  may  be  ordinary  iron  or 
steel  ship  anchors,  or  what  are  known  as  Chinese  anchors  (snrll  cribs  filled  with 
stones),  or  such  other  devices  may  be  used  as  the  localities  afford.  It  will  be 
found  advisable,  as  it  is  usually  most  convenient,  to  handle  the  pipes  and  make 
the  borings  at  one  end  of  the  scow  rather  than  through  a  well  in  the  center.  If 
the  Cunsnt  is  strong,  it  will  also  be  necessary  to  make  the  borings  at  the 
down  stream  end  of  the  scow.  The  pipes  are  projected  downward  from  the  handling 
frame  in  tho  manner  shown  in  the  figure.  In  order  to  hold  the  pipe  against  the 
current,  lines  or  cables  are  carried  from  the  upend  of  the  scow  underneath  it, 
around  the  pipe  and  back  again,  as  shown.  If  the  water  is  deep  or  the  current 
very  strong,  two  or  more  loops  of  the  line  or  crble  may  be  required.  In  the  manner 
described  and  by  the  means  indicated,  the  scow  can  be  held  stiffly  in  position  in 
almost  any  current  and  in  water  of  considerable  roughness,  although  when  the  water 
becomes  too  rough  it  is  necessrry  to  suspend  operations. 

Considerable  lateral  variations  in  the  position  of  the  scow  may  be 
secured  in  the  manner  shovm  in  Fig.  6,  without  moving  the  anchors.  If  the  cable  A 
running  from  one  corner  of  the  scov/  be  lengthened  while  the  others,  B,  be 
shortened,  the  scow  will  be  moved  laterally  to  the  position  shovm  by  the  broken 
lines  without  movement  along  the  current.  A  judicious  selection  of  position  for 
the  anchors  will  materially  facilitrte  the  operations  to  be  conducted1,  in  taking  a 
line  of  borings  .c-jcross  the  current. 

The  number  and  location  of  borings  will  depend  on  the  features  of  each 
particular  case  and  they  are  to  be  determined  by  the  judgment  of  the  engineer* 
For  a  location  of  a  break-rater  they  may  at  times  be  as  much  as  1000  ft.  apart, 
or  as  near  as  25  ft.  or  less  for  other  purposes. 

In  these  submarine  boring  operations  it  is  necessary  to  use  soniev/hat 
heavier  pipes  thrn  in  ordinary  jet  boring  work.  Three  to  four  in.  pipes  carrying 
an  inner  pipe  of  1  1/2  to  1  3/4  ins.  diameter  have  been  found  to  b e  very  satis- 
factory for  some  <^nr>  work  in  strong  tidrl  currents  or  the  Pacific  Coast.  Consult 


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25 

"Report  of  Board  to  Locate  a  Deep  V/ater  Harbor  at  Port  Los  Angeles  or  at  Port 
San  Pedro,  California,  1897";  Appendices  D  and  E;  also  Pis.  8,  9,  10,  11,  12. 
A  steam  pump  was  used  for  farcing  the  water  through  the  inner  pipe  and  operations 
were  conducted  in  water  50  ft.  deep  or  more. 

In  submarine  work,  as  in  borings  on  land  or  under  rivers,  it  is 
necessary  to  guard  against  being  misled  by  a  wrong  interpretp+ton  of  conditions 
at  the  bottom  of  the  pipe.  In  one  case  rock  had  been  reported  beneath  a  layer 
of  mud  and  sand  at  a  harbor  entrance  and  the  harbor  had  been  reported  as  being 
incapable  of  much  improvement  in  consequence  of  the  excessive  cost  of  removing 
the  supposed  rock.  At  a  subsequent  date  the  locality  was  more  carefully  examined 
and  it  was  found  thet  the  supposed  rock  was  little  more  than  a  layer  of  hard 
cemented  gravel  a  fev/  inches  only  in  thickness;  also  that  down  to  a  depth  of  at 
least  42  ft.  below  mem  low  water,  there  was  no  rock  whatsoever. 

Throughout  all  these  boring  operations  conducted  by  means  of  a  jet, 
or  in  boring  through  rock  by  whatever  process,  a  scrupulously  careful  record  of 
the  material  passed  through  should  be  kept,  and  in  boring  on  land,  the  elevation 
of  the  subsurface  water,  if  any  be  found,  should  be  observed  with  equal  care. 
After  complete  data  have  been  secured,  a  profile  pL°.n  should  be  made  showing  each 
boring  in  its  proper  location;  the  depth  to  which  it  was  carried  below  datum 
and  the  accurately  placed,  strata  of  all  material  found,  including  the  subsurface 
level  of  water.  This  plan  could  be  preserved  as  a  part  of .the  permanent  records 
of  the  contemplated  work;  see  Figs,  7A,  7B,  and  8. 

If  subaqueous  borings  through  rock  are  to  be  made,  the  diamond  drill 
or  other  rock  boring  process  must  be  employed.  (See  Diamond  Drill  Borings,  fiew 
East  River  Bridge;  Eng.  News,  Sept.  24,  1896,  Vol.  36,  p.  198),  For  this  purpose 
the  scow  on  which  the  boring  outfit  is  supported  must  be  held  much  more  exactly 
in  position  in  rough  water  than  is  required  for  jet  boring.  Specirl  means  and  a 
more  elaborate  frame  vork  for  handling  the  boring  appliances  will  also  be  needed, 
The  devices  required  will  depend  upon  the  degree  of  exposure  of  the  location  ~nd 


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26. 

other  local  features,  which  will  need  careful  consideration  for  the  conduct  of 
any  given  piece  of  work.  It  will  not  generally  be  practicable  to  conduct  these 
operations  in  as  rough  water  as  that  in  -which  jet  boring  may  be  done. 

Additional  References. 

1.  A  Treatise  on  Masonry  Construction;  1. 0. Baker,  10th  ed. ,  1909, 
.Chap.  XIII,  pp.  330-334. 

2.  A  Practical  Treatise  on  Foundations;  V/.il. Patton;  pp.  166-170,  Arts. 
25-27;  p.  373,  Art.  91. 

3.  Sewer  Design;  H.ft.Ogden,  Chap.  II,  pp.  18-24 

4.  Borings  in  Broadway,  N.Y,  ;  \7,B, Parsons,  Trans.  Am.Soc.C.E.  ,  Vol.  28, 
p.  13,  1893. 

5.  Apparatus  for  Obtaining  Borings  by  Direct  Pressure;  T.  Allen,  Trans 
Ani.  BOC.  C,E.  ,  Vol.  2,  p.  41,  1873, 

6.  Deep  Borings;  Eng.  Kev/s,  Apr.  13,1893,  p.  505. 

7.  Consult  General  Index,  Eng.  Hews,  1895-1899  1890-1904;  1905-1909; 
Borings  and  Drilling. 

8.  Sev/erage;  A,P,Folwell,  p.  109. 

9.  Explorations,  H.idson  River  Crossing,  Catskill  Aqueduct;  A,D»Elinn; 
Eng.  Kev/s,  Vol.  59,  p.  358;  Apr.  2,  1908;  see  Fig.  7A, 

10.  Diamond  Drill  Borings,  Olive  Bridge  Dam,  Ashokan  Reservoir;  Eng, 
Record,  Vol.  58,  p.  25,  July  4,  1908, 

11.  Memorial  Bridge  Across  the  Potomac  River;  55th  Congress,  H.  of  R 
Doc.  388,  1898. 

12.  Diamond  Drill  Boring  Costs;  Eng. -Contracting,  Jan.  9,  II" r.  13,  1907, 
April  29,  May  6,  1908;  April  21,  July  23,  Sept,  8,  190S ;  Jrn.  5,  1910, 

13.  Cost  Keeping  Systems  and  Blanks  for  Diamond  Drill  '.York;  see 
Cost-Keeping  and  Llanagenient  Engineering,  by  Gillette  &.Dana, 

14.  Diamond  Drill  Borings  for  a  Dam  on  the  Clackamas  River,  Oregon; 
Eng.  Kews,  Vol.  G4,  Dec.  22,1910,  p.  684. 

15.  Borings  for  the  Panama  Railroad  Dock  at  Cristobal,  with  table  of 
costs;  Eng.  Kev/s,  Vol.  63,  June  1C,  1910,  p.  691. 

16.  Profile  of  Spuyten  Duyvil  site  for  proposed  Kenry  Hudson  Memorial 
Bridge;  plans  showing  strata  ^nd  diamond  drill  borings  on  a  line  50  ft.  west 
of  asis  of  bridge;  Eng.  News,  Vol.  58,  p.  5£0,  i><ov.  21,1907  = 

17.  Inclined  Diamond  Drill  Borings  under  the  Hudson  River;  Eng.  Record., 
Vol.  61,  p.  G8,  Jrn.  15,  1910, 

18.  Recent  Practice  in  Diamond  Drilling  and  Borehole  Surveying;  J,I» 
Hoffman,  Eng.  Eev/s,  Vol.  68,  Aug.  29,  1912,  p.  404 

19.  Freitrg;  Architectural  Engineering;  Chap.  9,  FP-  284-309- 

20.  Drill  Outfit  for  Light  Blast  Holes  and  for  Rock  Soundings;  Eng. 

°21.  Pile'lests  Indicate  Type  of  Substructure  for  Technology  Building; 
Eng.  Record,  Vol.  72,  p.  235 


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22.  Geology  of  New  York  City  Revealed  in  Core  Boring  Exhibit;  by  H.  E. 
Zipser;  Eng,  Nees-Record,  Vol.  85,  p.  60 

23.  Foundations  of  Bridges  r.nd  Buildings;  Jacoby  &  Er.vis,  Chap.  17, 
p.  518,  Explorations  rnd  Unit  Lor.ds. 

24.  Engineering  and  Building  Foundations;  Fowler,  Chap.  12,  p.  232, 
Location  and  Design  of  Piers. 

25.  Practical  Treatise  on  Sub-Aqueous  Foundations;  Fowler,  Chap.  22, 
p.  424. 

26.  Ordinary  Foundations;  Fowler,  Chaps.  12  and  13,  p.  182. 

PROBLEMS 


1.  Tell  how  you  would  sink  a  test  boring  to  rock  by  the  water  jet 
process;  the  site,  a  river  location  for  a  bridge  pier;  the  probable  depths  of 
materials  in  order  being,  water  30  ft.;  silt  15  ft.;  mixed  sand  and  clay,  40  ft.; 
total  depth  85  ft,  to  rock.  Describe  the  apparatus;  give  sketches;  state  the 
precautions  to  be  observed  before  finally  interpreting  results. 

2.  Describe  method  of  sinking  a  foundation  boring  on  land  into  soft 
materials  requiring  casing  and  water  jet  process  for  30  ft.,  then  drill  boring, 
using  chilled  shot  process  in  order  to  penetrate  20  ft.  further,  to  be  certain  of 
rock  foundation.  Give  stale  sketches.  Consult  texts,  references  and  trrdc 
catalogues. 

3.  A  test  pile  penetrated  6  3/4"  totrl  under  the  last  five  blov/s  of  a 
3500#  hammer,  falling  freely  from  a  point  22'  above  the  head  of  the  pile.  If  the 
loss  of  hammer  energy  per  blow  is  estimated  at  Q%,  co^.ipute  the  probable  safe  load 
by  the  Engineering  weus  Formula  using  a  factor  of  srfety  of  4  instead  of  that 
involved  in  the  formula  given  in  the  Rotes.  If  the  material  penetrated  is  a 
viscous  mixture  of  sand,  clay  and  earth,  how  does  the  above  calculated  figure 
co-ipare  to  lo*d  ccpacitjr  one  month  after  driving? 


- 


:j     "  -     ? 


- 


;; 


28 

CHAPTER  2 

CIASSIFICATIOIT  OF  FOUKBATION  SOILS 

BEARING-  POVflER 

The  locction  of  important  engineering  works  is  influenced  by  such  varied 
conditions  that  it  razy  b3  necessary  to  construct   foundations   on  widely  different 
classes  of  rjateriai.   Kence,  a  general   discussion  and  classification  of  soils 

should  precede  a  detailed  study  of  the  design  of  foundation  types;  particular 

i 

reference  being  ;rade  to  tho  bearing  capacity  of  the  soil. 

A  classification  of  this  nature  must  be  mere  or  less  arbitrary,  and 
general  rather  than  specific.  The  different  kindscof  foundation  soils  grade  into 
each  other  so  gradually  that  the  classification  in  any  particular  case  is  fre- 
quently a  matter  of  individual  opinion  or  judgment.  Certain  materials,  such  a s 
hardpan  and  quick  sand  are  particularly  difficult  to  describe  accurately. 

There  is  no  line  of  engineering  work  in  which  there  is  mere  room  for  the 
exercise  of  judgment  and  exp?rionce  than  when  assigning  allowable  foundation 
pressures.  The  unit  soil  pressure  affects  largely  the  design  of  the  substructure; 
to  a  lesser  extent,  the  superstructure,  so  that  it  is  commonly  necessary  to  fix 
values  in  advance  of  the  design,  from  data  obtaired  from  test  boiings.  For 
important  structures  these  values  should  always  be  checked  where  possible  by 
direct  tests  of  the  bearing  pov.'cr  of  the  soil  after  the  foundation  excavations 
have  boon  made.  Such  tests  often  are  difficult  to  make  and  the  results  obtained 
so  uncertain  that  their  interpretation  requires  almost  as  much  judgnent  and 
experience  as  'would  be  needed  to  arbitrarily  fix  the  values  without  such  tests. 
^ny  material,  except  solid  rock,  will  yield  when  heavily  loddad,  especially  on 
such  small  areas  as  it  is  necessary  to  use  when  m.- king  tests.  This  yielding  \vill 
be;:in  under  moderate  loads.  It  is  a  matter  of  opinion  how  much  settlement  is 
allowable;  the  amount  being  largely  affected  by  tho  character  of  the  proposed 
structure. 

Foundation,  materials  listed  in  the  order  of  their  desirability  are:- 


.  .ri- 


.'      •  •  : 


-r.    . 

— .  •    .-.  •    •  •*  •          i  .^  . 

1   • .  ;  •    ..  •    -  -       - 


^J  *--->•"•"••'     - 

:  '.  x;  ' 


'•        •   "•' 


29. 

1.  Solid  rock 

2.  Grave  1  and  hardpan 

3.  Send 

4.  Clay 

5-  Ordinary  soils,  usually  riore  or  less  compressible. 
6.  Semi -liquid  soils  -  qyicksand, 

For  a  comprehensive  list  of  soils,  their  definition,  mineralorjical  compo- 
sition, characteristics,  color,  settlement,  laboratory  tests  ,  etc.,  see  Proc. 
Am.  Soc.  C.E. ,  Feb.  1921,  Progress  Report  of  Special  Committee  to  Codify  Present 
Practice  on  the  Bearing  Value  of  Soils  for  Foundations,  p,  11.  Consult  also  Proc. 
for  Aug.  1920,  Table  1  and  Plates  XI  and  XII  for  Bearing  Power  and  Loading  Test 
Apparatus . 

1.  SOLID  ROCK 

The  ultimate  crushing  strength  of  a  2-inch  cube  of  any  rock  hard  enough 
to  resist  the  wearing  action  of  running  v/ater,  when  t  ested  "by  a  standard  laboratory 
machine  is  at  least  180  to  200  tons  (of  2000  lb. j  per  sq.  ft.  The  h  ardest  and  . 
best  building  stones  v;ill  withstand,  for  selected  specimens,  2000  tons  per  sq. 
ft.  Consult,  Burr,  The  Elasticity  and  Resistance  of  the  Materials  of  Engineering 
1915,  seventh  edition,  Art.  69,  pp.  420-425, 

The  strength  of  masonry  blocks  in  large  masses  in  place  usually  is 
assumed  to  be  considerably  greater  than  that  of  2-inch  cubes,  since  the  stones 
are  prevented  from  yielding  laterally.  If  this  were  not  so,  high  rock  cliffs, 
such  as  are  frequently  found  in  nature,  like  El  Capitan,  Yosemite  Valley, 
could  hot  exist. 

As  tl>o  maximum  pressure  upon  any  footing  course  of  an  engineering  structure 
seldom,  or  never,  v/ill  exceed  ten  or  twelve  tons  per  sq.  ft.,  the  softest  stone 
will  give  a  safety  factor  of  nearly  20.  It  may  be  concluded  that  any  ordinary 
rock  foundation  bed,  v/hen  cleared  of  disintegrated  surface  material,  iscoapablc 
of  carrying  any  load  produced  by  an  engineering  structure  founded  upon  it. 

The  rock  should  first  bo  laid  bare  by  open  excavation,  or  excavation 
within  sheet  piling  or  cofferdams,  or  for  deep  foundations,  bgr  other  more 
difficult  methods,  such  as  pneumatic  and  desp-v/ell  dredging;  after  which  the  rock 


•* 


':  ."  • 


...    !  -vF . '-     ..         :'••:-. 


.   pflfe 


:(• 


•rs-.  -- .;- :      .,      ,    I" I,  ... :.  3SS:';    :': 

.-.  -  t ,.  ..  '.     : 


:.jLCii-.      jufcaxk;": 


30 

bed  should  bo  examined,  thoroughly  in  order  to  determine  the  shape  and  condition 
of  its  surface  and  its  general  character.  If  soft  spots  are  found,  or  if  tls  re 
are  crevices,  cracks  or  fissures,  filled  with  softer  or  rotted  raster ial,  they 
should  be  cleaned  out  to  their  deepest  points  ar.c.  filled  with  concrete.  All  soft 
rock  should  be  removed,  if  necessary  by  blasting,  so  that  perfectly  sound  and 
hard  material  is  exposed  to  receive  t  he  foundation  bed.  For  vertical  or  gravity 
loads  all  sloping  rock  should  be  roughly  benched  in  steps  with  treads,  5  to  8 
ft.  horizontal  or  sloping  slightly  backward  and  downward  and  with  vertical 
risers,  so  that  the  entire  surface  receiving  the  foundation  will  be  approximately 
at  right  angles  to  the  pressure  which  is  to  come  upon  it.  For  inclined  lodds 
or  thrusts,  as  in  arched  rib  abutments  or  retaining  wall  footings,  the  rock 
should  be  stopped  on  an  incline.  The  rock  surface  in  all  cases  should  be  so 
roughened  or  broken  that  the  footing  course  docs  not  rest  upon  a  perfectly 
smooth  surface,  unless  that  surface  happens  to  be  practically  normal  to  tie 
resultant  pressure.  The  main  end  to  be  attained  is  to  secure  a  perfect  bond 
between  the  footing  course  and  the  rock,  to  avoid  completely  any  possibility  • 
of  sliding  between  the  footing  course  and  the  bed.  Blasting  is  frequently 
resorted  to  to  clean  the  surface  of  the  rock;  it  has  the  advantage  of  not  only 
removing  all  loose  and  disintegrated  material,  but  also  of  leaving  the  bed 
rough  and  jagged  so  that  a  good  bond  may  be  secured  with  tiro  concrete. 

If  water  percolates  into  the  foundation  excavation,  it  should  be  pumped 
out  or  drained  away  by  some  method  which  will  enable  the  footing  course  a nd 
foundation  masonry  to  be  laid  dry  and  maintained  so  tmtil  the  mortar  is  'set, 
after  which  the  presence  of  water  in  the  material  overlying  the  rock  may  be 
disregarded  so  far  as  any  effect  upon  the  foundation  is  concerned.  Sometimes  it 
is  impossible  to  remove  the  water;  in  such  cases  at  least  the  lowest  part  of  the 
substructure  must  be  laid  umer  water.  The  methods  to  bo  usod  are  treated  later 
in  Chapter  8. 


.  iff 


r;x    .o:':>..; 


•.•!•<•   :-- 

'.  .  '.. 


>-..'    pcf  Li'cooo    ..=,::.; 


-i;     * 


aorr 


31 

2.  GRAVEL  AHD  HARDPAN 

"Hardpan"  is  a  compact  or  cemented  gravel,  composed  of  irrogulat  stones, 
of  all  sizes,  mixed  with  clay  and  sand,  the  latter  filling  the  voids  in  the 
gravel.  The  torn  is  also  rather  loosely  applied  to  indurated  clay,  which  usually 
occurs  mixed  with  sand.  Hardpan  grades  off  on  one  hand  into  cemented  gravel 
or  hard, compact,  conglomerated  rock.  On  the  other,  it  passes  through  indurated 
clays  containing  smaller  and  smaller  proportions  of  grr.vel  and  dand,  to  a 
clr.y  which,  on  exposure  to  air  and  water,  may  become  soft  and  unreliable.  A 
material  of  this  nature  is  liable  to  occur  irregularly  in  valleys  formed  by 
sv/ift  silt -bearing  rivers.  It  is  deposited  by  sudden  freshets  at  the  mouths  of 
crooks  or  tributary  streams,  and  when  mixed  with  sand  and  clay  becomes  in  time 
very  hard  and  compact.  It  frequently  is  so  hard,  approaching  the  condition  of 
natural  concrete,  that  it  is  necessary  to  resort  to  blasting  before  it  can  be 
excavated,  even  with  heavy  dredging  machinery. 

If  there  is  a  sufficient  volume  of  hardpan,  it  makes  an  excellent  found- 
ation bed.  It  is  apt  to  occur  in  rather  thin  layers;  often  between  strata  of 
seni-liquid  sand  or  silt.  Borings  for  bridge  piers  in  the  Mississippi  Valley 
have  oBten  disclosed  such  examples.  Consult  Report,  The  Memphis  Bridge,  by 
George  S.  Morison.  Compact  grr.vel,  without  cementing  nnterial,  also  will  gifce  a 
perfectly  satisfactory  foundation.  The  gravel  is  best  v/hen  coarse  a,"d  finer 
particles  are  intermixed  to  leave  as  siT^all  a  percentage  of  voids  as  possible. 
Layers  if  gravel  ttro  feot  >r  more  thick  and  well  compacted,  rti.ll  bear  very  heavy 
loads,  even  thopgh  overlying  poorer  material.  Adequate  foundations  can  be 
secured  sometimes  by  dumping  gravel  into  quicksand,  or  into  boggy  or  marshy 
la^d,  when  nothing  else  vd.ll  suffice,  though  this  is  liable  t?  cause  the 
adjacent  land  to  rise.  Gravel  has  the  advantage  over  s and ,  for  as  the  grains 
become  larger,  it  has  a  greater  resistrnce  to  running  or  percolating  water.  This 
is  expecially  true  if  the  gravel  is  mixed  with  a  sand  or  clay,  vhich  prevents 
water  seeping  through  it.  Compact  grr.vel  will  safely  bear  from  8  to  15  tons  per 
sq.  ft.  A  Brooklyn  Bridge  Pier,  vdth  a  pressure  of  5  1/2  tons  per  sq.  ft.  is 


.'"  3       ' 


V    t: 
.-.  j    ?-i  ......  •    .jjj 

:"  c^  iiosc'-s  -.  "fi  aci'l  «O^OT:O     • 


:o*1o   ;2r,-''-;"w  .  •=  1  ^.1 

^ 
•  :"  ->••<*  CET  •  ;•: 

.  r    . 

;  '-'        ;:  •  -        '-'  ''.".•:. 


.      ffl  .  •;; 

--          r^    .:£    «.    .i- 


32 

founded  on  a  two-foot  layer  of  cor.ipact  gravel,   overlying  rode. 

5.   SAKE. 

Sand  can  be  divided  into  three  general  classes,  according  to  its  chemical 
composition. 

a.  Argillacious  sand  is  forrrad  by  the  disintegration  of  clay,   slates  and 
shales.   If  very  fine,    or   thoroughly  disintegrated,   it  grades   into  clay.   If  the 
grains  are  granular  or  hard,    it  may  be  called  sand,   though  it  is  the  poorest 
kind  of  sand  for   founiation  purposes. 

b.  Calcareous  sand  is  used  for  making  hydraulic  cement,  but  is  not   fcund 
commonly.   It  is  formed  by  the  disintegration  of  lime  rocks.    It  is  a  poor 
material  for  foundations,   liable   to  decompos  e  after  exposure  to  air  and  to 
moisture. 

c.  Siliceous   sand   ,   composed  principally  of  a  lica,   is  more  common  than 
any  other,  and  makes  a  nuch  more  satisfactory  foundation  bed.  The  strata  should 
be  reasonably  thick  and  extensive  in  area.   Coarse,  angular  river   sand  is  better 
than  water-worn  rounled  sea  sand. 

It   is  stated  often  that  high  grade  siliceous  sand  will   support  any 
practical  load  if  the  sand  car.  be  held  laterally.  V.Tien  securely  retained  it  is 
nearly  incompressible.    It  has   been  leaded,   confined  in  trenches,    to  100  tons 
per  sq.    ft.     V/here  difficulty  has  been  experienced  with  sand  foundations,    it 
has  usually  been  due   to   the   tendency  of  the  material,  mixed  with  water,    to 
act  under  the   laws  of  hydraulic  pressure,  yielding  in  any  direction  along  the 
line   of  least  resistrnce.   Sane1.,    if  compact  and  well  drained,   especially  if 
mixed  with  a  cementing  material,   such  as  a  small  percentage   of  clay,  oay  grr.de 
into  hardpan,    intermediate  in  supporting  strength  to    sandstone.   Sand  is  porous 
and  unless  confined  between  clayey  rocks   or  by  artificial  barriers,  water  may 
pass  through  and  scour  it,  undermining  the  structure  above  it.  The  process   of 
scouring  is  greatly  aided  by  the  pressure  from  the   abnormal  loads  transmitted 
to    the  sand  by  the   foundation.   If  an  excess  of  water  is  present,   especially 
if  the   sand  grains  are  find  ar.d  well  rounded,  a  quicksand  results  which  has 


33. 

little  or  no  bearing  power,  unless  prevented  from  spreading  laterally.  The  coar- 
ser the  grains  of  sand,  the  less  the  danger  of  scouring  and  the  greater  is  the 
bearing  resistance. 

It  is  especially,  advantageous  to  carry  foundations  in  sand  to  a  consider- 
able depth.  The  sand  $ill  then  be  more  compact  because  in  its  natural  position 
it  is  subject  to  a  greater  overlying  loac  .  There  "frill  also  be  less  possibility 
of  lateral  spreading  or  exposure  to  running  or  percolating  water. 

In  general,  if  sand  can  b e  drained  and  confined,  it  will  safely  hold 
from  2  to  15  tons  per  sq.  ft.  The  Chicago  Building  La'  s  permit  2  tons  per  sq. 
ft.  on  dry  sand  in  strata  15  ft.  or  more  in  tMckness.  Pressures  from  2  to  2.5 
tons  per  sq.  ft.  are  allowed  in  Berlin  for  buildings  founded  on  sand  or  sandy 
soil.  The  Washington  Monument,  555  ft.  high,  with  a  foundation  pressure  of  11 
to  14  tons  per  sq.  ft.  is  founded  on  a  layer  of  fine  sand  2  ft.  thick.  The  San 
Francisco  Building  Ordinance,  section  57,  allows  3  tons  per  sq.  ft.  on  loam  or 
fine  sand,  4  tons  on  co;npact  sand. 

4.  CLAY 

I 

Clay  is  formed  from  the  disintegration  and  deposition  below  water  of 
aluminum  rocks,  ar..d  is  one  of  the  commonest  materials  found  in  nature.  It  varies 
greatly  in  character,  passing  grrdually  from  slate  to  shale,  to  indurated  clay, 
to  soft,  samp  or  wet  clay,  and  finally,  with  an  excess  of  water,  to  a  semi- 
liquid  material,  which  yields  in  all  directions  to  pressure,  and  will  flow  almost 
like  water.  The  percentage  of  voids  is  larger  than  in  almost  any  other  material, 
b$-b  they  are  exceddingly  fine,  so  '.hat,  while  clay  is  usually  almost  impervious 
to  running  water,  it  v/ill  slowly  absorb'  large  quantities  of  vater  and  become' 
semi-liquid  in  time.   Clay  normally  contains  much  water ,  some  of  which  it  is 
impossible  to  remove.  If  allowed  to  freeze,  it  expands  with  a  "  bearing"  effect 
upon  imbedded  foundations.  In  cold  climates  it  is  necessary  to  carry  the  foun- 
dation well  below  the  frost  line  or  cracks  end  unequal  settlements  will  develop. 
Dry  clay  rapidly  absorbs  moisture,  even  from  the  air,  and  'swells,  attended  with 


34 

great  pressure.   Disastrous   effects  have  sometimes  resulted  from  ramming  dry 
clay  behind  retaining  walls.   Railroad  embankments   or  levees   built  of  wet   clay 
may  be  seriously  endangered  by  the  formation  of  large,   deep   cracks  as  the 
material  drys  out. 

The  Calaveras  dam-    liquid  clay  core,  which  caused  the   failure  in  Alarch 
1918,  was  very  wet  and  supersaturated1.   Samples     of  this   flowing  clay,  when  most 
liquid,  gave  percentages  of  moisture  by  weight    from  50.0  to  56.6  percent;   or 
73  to  77  percent  moisture  by  volume.   This  clay  core  therefore  was  an  emulsion 
containing  about  39%  finely  divided  clay,   tho   -est   of  tte    volume  being  water. 
Samples  of  air-dried  material  from  the  top  of  the  clay-ppol  in  the  destroyed 
dam,  when  cut  out  and  e xamined,   contained  on  an  average  about  35%  voids.        In 
other  words  when  baked  dry  by  the  sun  the  clay  had  65%  by  volume  of  solids   iri  it 
instead  of  the  30%  in  the   original  emulsion  or  supersaturated  -material. 

.    * 

The  least  compacted  material  remaining  in  position  in  the  dam  a  fter  the 
slip  contained  from  45   to  50%  voids.    See  an  article  by  A.   Hazen  "A  Study  of  the 
Slip   in  the  Calaveras  Dam";   Engineering  liews-Record,   Vol.    81,  p.    1158. 

'»  - 

In  general,  wet  clay  is  very  treacherous  and  unreliable,    so   that 
foundrtions   constructed  upon  this  material  should  be  thoroughly  drained,    if 
possible,   and  water  nc»j  allowed  to   stand  on,    or  especially  to  run  over,    them  as 
some  clays  are   very  easily  washed  away  by  running  v;ater.      On  account  of  the 
expanding  effect,    it    is   absolutely  necessary  that   foundations  must   be  kept    from 

| 

being  alternately  wet  and  dry.   If     foundations  must  be  established  in  under- 
drained  clay,    every  .precaution  should   be  taken  to  prevent  the  material  from 
oozing  or  flowing  away  laterally,    especially  into  adjacent   foundations.   The 
material  tends  to   flow  in  .all  directions.    In  deep  railroad   cuts,   or   similar 
construction     in  soft  clay,   the  weight  and  pressure  on  the  sides  tends  to  make 
the  bottom  rise,  the  effect  being  especially  marked   in  cofferdams   or  caissons, 
where   the  sides  are  held.  Excavations  for  tunnels,   trenches  and  alafts  tend  to 
close    in  on  all  sides  slowly,   hence  they  should  be  made -larger  than  ultimately 


35 

required.  When  beds  of  clay  occur  in  definite  strate,  inclined  at  any  consider- 
able angle,  especially  if  resting  on  tipped  rock,  the  problems  presented  are 
extremely  grave.  Percolating  water  tends  to  fill  the  contact,  or  stratification 
planes,  causing  the  whole  mass  to  slide.  This  tendency  has  given  much  trouble 
at  the  Panama  Canal,  and  has  been  the  cause  of  the  failure  of  irany  retaining 
walls.  It  is  sometimes  impossible  to  prevent  the  sliding  of  Icrge  masses  of  clay 
along  inclined  stratification  planes.  Slidings  of  this  sort  .nay  be  so  extensive 
that  the  pressure  will  gradually  tip  over  the  strongest,  haaviest  retaining  v/  alls 
The  only  remedy  in  such  cases  may  be  to  keep  removing  the  material  as  fast  as  it 

slides  and  until  a  condition  of  stability  or  equilibrium  is  reached. 

i 
Clay  is  so  variable  in  quantity  and  behavior  that  it  is  one  of  the  .  . 

most  difficult  materials  to  judge  and  v/ith  which  to  deal.  If,  instead  of  pure 
clay,  we  have  clay  mixed,  with  coarse  sand  orgravel,  or  both,  it  is  one  of  the 
b^st  foundation  materials.  The  Capitol  at  Albany,  15.  Y.  is  founded  on  blue  clay, 
containing  from  60  to  90  percent  of  alumina,  the  balance  fine,  siliceous  send. 
The  supporting  power-,  under  tests,  exceeded  6  tons  per  sc.  ft.,  the  safe  load 
being  assumed  2  tons  per  sr  .  ft.  The  Congressional  iibrery  at  \7ashington  ,  D.  C.  , 
is  founded  on  yellow  clay  mixed  v/ith  send.  The  ultimate  supporting  power  v«,s 
13.5  tons  per  sq.  ft.,  the  safe  load  taken  at  2.5  tons  per  so.  ft.  The  Missouri 
River  Bridge  at  Bismarck,  South  Dakota,  gave  an  ulti  -ate  bearing  strength  of 
15  tons  per  sc.  ft.  At  Chicago,  the  safe  bearing  power  for  buildings  founded  on 

^/ 

thin  layers  of  clay,  hard  above  and  soft  be-low,  resting  on  thick  layers  of  quick 
sand,  is  taken  at  1.5  to  2  tons  per  sq.  ft.  In  general,  the  safe  pressure  for 
thick  beds  of  clay  ccn  be  assumed  about  as  follows: 

If  always  dry,  from  4  to  6  tons  per  sq.  ft. 

If  moderately  dry,,  from  2  to  4  tons  per  sq.  ft. 

If  wet  and  soft,  fror;  1  to  2  tons  per  sc.  ft. 


•L.  OSDIEABY  SOIJt 
Under   this    heading   is    included  a  con  si?.  erable  variety  of  sedimentary 

soils,  usually  co:npose\d  of  mixtures   of  clay  and  send,    in  all  proportions,    or 
very  fine    send,   also  certain  varieties  of  black  or  blue  clays  containing  con- 


36 

siderable  organic  matter,  frequently  known  by  local  terms,  such  as  "adobe",  or 
"gumbo"  soils.  These  are  materials  most  commonly  found  in  valleys  built  up  by 
sedimentary  deposits  from  river  action.  Similar  conditions  result  in  most  coast 
cities  when  a  portion  of  their  area  is  compos?1  of  artificially  filled  land,  as 
the  water  front  is  gradually  advanced.  Such  materials  are  less  uniform  than  soil 

*  / 

normally  formec",  more  compressible  and  unreliable.   They  are  quite  apt   to  slowly 
settle  under  the  prolonged  action  of  their  own  weight  and  may  suddenly  settle 

A  t 

a  considerable  amount  from  violent  earthquake  shocks.  These  materials  are  com- 

/ 
pressi ";le  so  that  foundationsbearing  heavy  loads  are  apt  to  settle  slowly  through 

them.   This  settlement  is  not  particularly  injurious  if  it  occurs  uniformly 
underneath  an  entire  structure.  To  insure  equal  settlement  it  is  necessary  to 
have  the  unit  soil  pressure  under  different  portions  of  the  entire  structure 
uniform  if  the  soil  is  uniform.  To  insure  this  condition  upon  a  varying  material 
where  for  example  a  large  building  rests  on  a  soil  of  changing  composition, 
requires  viuch  study  and  analysis;  a  subject  which  is  trpated  in  considerable 
detail  in  Chapter  4° 

In  Chicago  high  buildings  founded  on  thick  beds  of  clay  and  sediment 
soil,  &ry  above  and  wet  below,  have  settled  as  much  as  3  or  4  inches,  in 
extreme  cases,  even  6  inches  without  damage  to  the  buildings.  It  is  necessary  to 
have  the  foundation  bed  homogeneous  throughout  for  each s tructure,  otherwise 
unecfual  settlement  will  occur,  causing  the  foundation  to  tip  or  crack.  This  is 
much  more  important  for  tall,  narrow  structures  such  as  chimr.0ye  and  towers  than 
for  massive  buildings  or  heavy  foundations,  such  as  are  required  for  docks  or 

quaywalls. 

EARTH  PHLSLUT.S  IK  SOILS. 

For  sediment  soil,  or  clay,  and  to  a  limited  extent,  for  the  softer 
soils  considered  later,  a  mathematical  analysis  f.-\r  pressures  transmitted  in 
granular  masses  can  b  e  made  which  will  assist  in  determining  the  allowable  loads. 

-) 

For  material  like  dry  send  or  the  ideal  mass   of  granular  earth  whose   grains  are 
held   in  equilibrium  by  the  force   of  frictiononly,   a  formula  expressing  the  proper 


37 

depth  of  foundation  for  a  given  load  intensity  can  be  written  in  accordance 
with  Eankine's  theory  of  earth  pressure.      If  w  is  the  w  eight   in  Ibs.  per  cu.    ft. 
of  earth,  x  the  depth  in  feet  from  a  horizontal  ground  surface,  and  p  the  great- 
est  load  in  Ibs.   per  sq.    ft.  which  can  be  placed  upon  the  horizontal  earth  bed 
at  the  depth  x  without  disturbing  or  lifting  the   surrounding  material,    then, 
see   fig.   9,  } 

P  = 


l+sin0)"'  =  TO  (1+sin  0'))2  -------  •  -  ----   (1) 


(l-sin0)  (1-  sin  0} 

here  px  =  v/x  (1+sin  0J_ 
(1-sin  0) 

~t 

Consult  Rankine's  Mechanics,  Art.   199,   p.   219,   13th  ed.  ,   1901.     The 
angle  of  repose  of  the  material  is  0".     Table   I  shov.'s  the   values  of  p  for  0" 
betv.-een  5°  and  33*42'. 


i 

TABLE  I 

p 

5° 

1.418 

vx 

1O 

2.017 

v:x 

15 

2.885 

voc 

20 

4.16 

T.-X 

25 

6.07 

\vx 

30 

9.00 

v;x 

35°42' 

12.20 

-wx 

C.   Prelini,   in  his  book  "Earth  Slopes,  Retaining  'Vails  and  Dams"  gives 
a  good  elementary  treatment  of  the  effect  of  cohesion;   see  pp.    1-27.   Examine 
also  Cain's     later  v:ork  "Earth  Pressure,   Walls  s  nd  Eins",  Chap.   1,  pp.   1-26. 
The   limitations  of  earth  pressure  theories,   such  as  Rankine's  are  excellently 
portrayed  by  an  article  by     H.    G.   Moult on,    entitled,   "Earth  and  Rock  Pressures" 
Trans.  An.    Inst.  Mining  Engineers,   Feb.   1920;   this  paper  bears  particularly 
upon  the  problems  of   tunnels,  deep  excavations,  mining,   etc. 

Small  angles  of  repose  are   found  v/ith  vet  material;   foi    that  reason  , 
Table  I  shov;s  hov:  important   it   is  to  have  a  foundation  bed  dry.   The  angle   of 
repose,  33°42'    is  that   far  the  standard  slope,   1  1/2    :   1.  While  formula   (1) 
cannot  be  relied,  upon  always  to  give  practical   value;,    it  may  be  used  v.isely  and 

^f 

prudently  to  guide  the  engineer's  judgment. 


.,.,-  .-        ;.    - 


38. 

The  formula  neglects  the  cohesion  of  the  material  and  usually  gives 
results  too  lov;.  In  New  Orleans  and  other  cities  similarly  situated,  the  foundat- 
ion pressures  in  common  use  are  greater  than  v.'ould  be  indicated  by  the  formula. 
For  a  further  discussion  of  the  assumptions  upon  which  such  formulas  as  (1)  are 
based,  consult:-  Practical  Designing  bf  Retaining  Walls,  by  V/m.  Cain,  Van  Nostrand 
Science  Series  Ko.  3,  pp.  1-16.  See  also,  Church,  Mechanics  of  Engineering, 
edition  1909,  part  IV.  Chap.  3,  Earth  Pressures  and  Retaining  \Valls,  pp.  572-585. 

The  Building  Laws  of  Chicago  permit  a  maximum  load  of  4000  Ib.  per  sq. 
ft.  when  the  soil  is  a  layer  of  dry  sand  15  ft.  or  more  in  thickness,  v.'ithout  a 
mixture  of  loam  or  soft  foreign  substance;  or  3000  Ib.  per  sq.  ft.  as  a  maximum 
intensity  v/hen  the  soil  is  a  mixture  of  clay  and  sand,  the  foundation  in  no  case 
to  extend  less  than  4  ft.  below  the  ground  surface.  Assuming  the  mixture  of  clay 
and  sand  to  weigh  100  Ib.  per  cu.ft.  and  talcing  0  =  33"42',  Table  I  shov/s  that 
the  ultimate  supporting  power  of  such  a  material  at  a  depth  of  4  ft.  is  4880  Ib. 
per  cu.ft.;  consequently  an  allowed  pressure  of  3000  Ib.  corresponds  only  to  a 
1.6  safety  factor.  This  latter  value  is  too  small,  settlement  is  likely  to  take 
place.  At  a  depth  of  10  ft.  Table  I  shov/s  a.Tiple  sustaining  'power  for  the  same 
niaterial,  but  there  is  no  assurance  of  freedom  from  snail  settlement  as  time 
elapses,  in  consequence  of  the  load  squeezing  out  the  water  or  from  slow  subsid- 
ing motions  due  to  other  causes. 

6.  SEMI-LIQUID  SOILS 

Quicksand.   Semi-liquid  soils  include  soft,  marshy  and  alluvial  deposits 
composed  usually  of  fine  sand,  and  clay  intermixed  with  agricultural  mold,  or 
hunras,  and  saturated  with  water.  Such  soils'  are  found  along  the  sea  coast,  at 
stream  mouths,  along  lake  or  river  banks ,  and  in  river  deltas.  The  particles  have 
little  or  no  permanent  cohesion;  therefore  the  soil  has  snail  bearing  power, 
lailroad  embankments  or  levees  constructed  on  soft  marshy  ground  of  this  character 
u-o  liable  to  settle  slowly  for  long  periods  of  time.  It  is  important  to  have 
flat  side  slopes  in  Order  that  the  foundation  area  may  be  increased  and  the  unit 


. 


.-. 


'  r 

, 


:.'       V 


.......  .      . 

*•         •      <J.  ;         .  .'  :"':  ;           .*"•'"• 

-.'ft'      ..    .  .  .. 

-  '*••    ^*'            •*  '-'       '••'  •   '    f  .: 


nbi 


.li^S  arfT 
R£  8  ai  Ilos  sifc?  nad-. 


nr 


. 


I  '  .r.  1. 1 . 

'       :..:.«t'? 

" 


-  JA    .031 

3i   OT          '    I 


^cto  5 


0  ^Ilf. 

-    f'.r 


; 


39. 

pressure  correspondingly  decreased.  Settlement  is  frequently  accompanied  by 
rising  or  bulging  of  the  soil  adjacent  to  the  feet  of  such  structures.  This  danger 
may  be  greatly  increased  where  einbanlmients  or  levees  are  built  v/ith  dredges,  by 
the  location  of  the  borrow  pits  too  close  to  the  embankment.  This  is  especi&lly 
tKue  in  levee  construction  if  the  borrow  pits  are  placed  on  the  inside. 

Such  ground  generally  requires  special  treat, nent  before  it  will  support 
important  structures.  If  possible,  foundations  should  be  sunk  through  it  to  more 
stable  material  underneath.  Piles,  steel  or  pneumatic  caissons,  masonry  wells  and 
similar  structures  are  used  to  attain  this  purpose.  When  foundations  are  sunk  or 
floated  so  to  speak  in  semi-liquid  soils  alone,  a  major  part  of  the  supporting 

? power  for  the  foundation  comes  from  skin  friction  exerted  as  the  sjdes  of  the 
sub-structure  tend  to  sink;  kence,  the  lateral  area  exposed  by  the  foundation 
should  be  made  as  large  as  possible.  The  efficiency  ofa  pile  foundation  on  marshy 
ground  depends  primarily  on  skin  friction.  The  piles  are  driven  very  easily, 
especially  if  kept  in  continuous  downward  motion  by  light  but  rapid  blows  of  the 
hammer.  After  a  period  of  rest,  however,  which  allows  the  mud  or  silt  to  close  in 

\  around  the  piles,  the  foundations  can  be  settled  or  the  indifidual  piles  settled 

!  only  v/ith  the  ~roatest  difficulty.  In o xtreme  cases  of  excessively  liquid  silts 

! 
it  may  be  necessary  to  depend  chiefly  on  the  buoyant  effect  of  the  material.  The 

•  heaviest  structures  could  be  const,  ucteii  even  on  water  if  rafts  were  built  large 
i  enough  to  float  them;  the  same  principle  applies  in  a  measure  to  semi-liquid 

soils.  Formula  (1)  of  the  previous  article  could  be  adapted  to  the  extreme  con- 
j  ditions  of  floatation  for  semi-liquid  soils  by  making  the  angle  of  repose  zero, 
1  in  which  case  the  formula  becomes  p  =  wx,  the  same  as  for  hydraulic  pressure  on 

submerged  surfaces.  Hence  under  the  vorst  possible  conditions  the  poorest  material 

is  able  to  support  by  flotation  alone  nearly  twice  as  great  a  load  as  could  be 
|  supported  on  water  because  its  weight  per  cu.  ft.  is  nearly  twice  as  great.  It 
'  should  be  noted  that  both  skin  friction  and  buoyancy, -vary  directly  with  the  depth. 

of  foundation. 


40. 

A  serious   objection  to    this  class  of  foundations    is  that   they  may  con- 
tinue to  sink  slowly  for  many  years,   as   in  New  Orleans   and   San  Francisco.   Consult 
also  the  experience  at  the  Lucin  Cut-off : '  S.P,H,R. ,   Salt   Lake  Division.   In  San 

x 

Fraraisco  the  old  fipevills  swamp  which  extended  inland  to  Market  and  Seventh 
Streets,  and  along  most  6$  the  water  front  mainly  to  the  south  of  the  Ferry  Bldg. 
has  been  sinking  gradually  at  a  rate  of  from  one-half  to  two  inches  per  year.  In 
this  swamp  particularly  in  Islais  Creek  Basin,  marked  subsidence  occurred  at  the 
time  of  the  greet  earthquake  in  April,  1906, 

The  term  "quicksand"  is  not  easily  defined,  but  is  applied  commonly  to 
very  finely  powdered  or  divided  sand  mixed  with  water,  the  mfc ture  sometimes 
containing  a  small  percentage  of  clay  or  very  fine  silt,  such  as  would  be 
deposited  only  in  quiet  water.  Almost  any  vary  finely  pulverized  substance  when 
saturated  will  flow  under  pressure  like  water.  Quicksand,  confined  in  place, 
often  gives  indication  from  test  borings  like  that  of  a  solid  compact  material. 
When  exposed  to  air  and  water,  it  will  flow  indefinitely  and  transmit  great 
pressures.  Strata  of  euicksan?.  sometimes  are  found  of  great  d  imens ions  or  such 
extent  that  they  are  very  difficult  to  drain  or  to  penetrate  by  an  open  excavation 
especially  when  occurring  at  any  considerable  depth.  Strata  of  cuicksand  may 
be  unexpectedly  penetrated.  In  such  cases  they  slowly  flow  into  an  open  excavae- 
tion,  causing  the  superincumbent  material  to  settle,  crushing  the  walls  of  an 
excavation,  or  at  least  throwing  them  out  of  line.  It  is  soneti.ies   possible  to 
stop  the  flow  by  very  heavy  bracing  and  sheeting,  with  a  generous  use  of  brush, 

s 

straw  or  burlap. 

Where   it  is  necessary  to  penetrate  strata  of  quicksend  to  any  consider- 
able depth,   resort   is  had  frequently  to  one  or   two  processes,  which,   though 
expensive,  are  certain  of  success.    In  the  "Poetsch"   freezing  process    (consult 
Baker's  Masonry  Construction,  Arts.   909-913,   p.  455;    10th  ed. ,   1909)   a  proposed 
shaft   is  surrounded  by  a  series   of  pipes  eight  to  ten  inches   in  diameter,    inside 
of  which  are  inserted  similar  pipes  com  .Tunica  ting  directly  with  a  tank.  A  freezing 


•;       '-   ".  .     - 


'  41. 

liquid  is  circulated  by  pumping  through  the  smaller, pipes  freezing  the  soil  in 
the  form  of  increasing  cylinders  around  each  pipe,  \vhich  gradually  unite,  forming 
a  solid  frozen  v/all  enclosing  the  shaft,  or  the  entire  space  eventually  may  be 
frozen  solid.  The  frozen  material  can  be  excavated  by  ordinary  methods,  frequently 
requiring  no  bracing*  The  method  is  expensive  because  it  is  necessary  to  keep  the 
material  frozen  during  the  entire  progress  of  the  ivork.  It  seems  to  have  had  a 
rather  limited  application,  donfined  principally  to  the  sinking  of  shafts  for 
mining  operations,  principally  in  Germany,  and  has  not  been  used  to  any  extent  . 
in  this  country.  Consult  Eng.  Record,  July  16,1910,  Vol.  62,  pp. 62-69,  giving  a 
description  of  the  use  of  t ha  freezing  method  for  tunneling  the  Metropolitan 

Subway  at  Paris.  £,ead  Patton,  "A  Practical  Treatise  on  Foundations,  ed.  1906, 
Arts.  54  and  55,  pp.  332-342.  Read  Jacoby  &  Davis,  Art.  128. 

In  the  second  method,  the  area  to  be  excavated  also  is  surrounded  v:ith 
pipes,  v.'hich  need  not  be  more  than  1  to  2  inches  in  diameter,  and  Portland  cement 

0 

grout  is  forced  under  pressure  into  the  material  surrounding  the  pipes.  As  the 
cement  sets,  it  forms  v.'ith  the  quicksand  a  solid  mass  v/hich  can  be  excavated. 
It  is  sometimes  necessary,  before  injecting  the  cement  grout,  to  establish  a 
fafee  circulation  betv/een  the  bottoms  of  the  pipes  by  pumping  v.ator  into  alternate 
pipes  and  allov/ing  it  to  rise  in  the  adjacent  ones.  This  method  has  the  advantage 
over  the  preceding  one  of  requiring  a,  simpler  plant  and  of  permanently  solidify- 
ing the  -material.  This  principle  may  be  successfully  used  to  solidify  gravel  and 
boulders  dumped  und-ir  v.ater  to  form  a  foundation  for  a  dam  or  other  heavy  struc- 
ture. It  has  been  repeatedly  proposed  for  solidifying  sand  and  boulders  found  in 
place  in  the  beds  of  sv/ift  bearing  streams  to  form  a  permanent  foundation  for 
impounding  dav.s  or  diverting  v/eirs.  It  may  readily  ma'::e  -possible  the  construction 
of  important  structures  in  the  beds  of  sv.'ift  bearing  streams  under  conditions 
heretofore  deemed  prohibitory.  The  chief  difficulty  to  be  encountered  in  such 
casos  comes  from  the  compactness  of  the  material  as  found  in  place,  a  difficulty 

d 

v.'hich  it  ought  to  be  possible  to  overcome  by  the  use  of  substantial  pumping 


•  42 

machinery  to   force  the  cement  grout  at   considerable  pressure   into  the  surrounding 
material. 

In  alluvial  semi-fluid  river   silt   or  quicksand,    loads   of  from  one-half 
to  one  ton  per   sc  .    ft.   cm  be  appliod  \vith  s.-sall  settlement.   The  bearing  paver 
of  the  material  as  shov.Ti  by  .•.lathematical  an**  ."sis    is  dependent  largely  upon  the 
depths  to  -.-Inch  foundations  are  carried. 

METHODS  OF  HjgHMSIMi  TEL  BLAHILG  PO'TER 


OF  S/iRTH  FOUNDATIONS 

» 

1.  Depth;  sea  discussion  (fig.  9) 

2  «  Dra  inage 

3.  Confinement 

4.  Sand  Piles 

5.  Stock  Ramming 

6.  Sand  Layers. 

DRAINAGE  AIJD  CONFIEEuEL  T 

The  bearing  povrer  of  clay,    sand  or  sediment  soil   is   increased  greatly 

i 
by  drainage.  As  tho  v/ator  is  v/ithdrav/n,   the   bearing  pov:er   is   improved.   Surface 

rater  can  be   excluded  from  a  foundation  bed  b}-  using  surface  or  subsoil  drains, 
laid  st  the  bottom  of  a  trench  'surrounding  the   structure,   backfilled  v'ith  gravel 
or  other  porous  material.  Common  unvitrified  agricultural  or  drain  tile   (simple 
C3'lindors  vith  plain  ends,   usually  in  1  ft.    lengths)    should  be  used  at   the  bottom 
of  the  t  rcnch  at   1;  vcls    somov/hr.t  bolov:  the   foundation  footings.  This  is   a  common 
procedure  for  v/alls   of  buildings.  The  exclusion  of  underground,   or  percolating 
v.Titer  is   often  a  more  difficult  problem,   especially  if  the  v.atcr  rises  under 
pressure   from  bcloir;.    It   ie  very  important  that  the  problem  be  solves,  especially 
for  clayey  soils  or   fi'nc  sand.    If  thoro   is   evidence   of  vat  or  percolating  from 
below  oror  an  entire   foundation  bed,  a  layer  of  coarse   grovel  c  an  be   spread  below 
the    foundation  and  a  system  of  opcn-jointoc!  tile  drains   imbedded  vheroin  to  lead 
off  the   vator.    If  the  percolating  \.ater  comes   laterally  from  higher  ground,    or 
follows  horizontal  scams,   trenches   filled  v:it>  coarse   grr.vol  and  the  drains  may  b 
dug  around  the   foundation  site  as  described   for  the  exclusion  of  surface  v;atcr. 
oomcti.nos   instead  of  filling  the   trenches  \vith  g;avol,   they  are  backfilled  v.'ith 


43.  • 

an  impervious  material,  such  as  puddled  clay  or  concrete,  tiles  being  laid  at 
the  bottom  of  the  trenches,  and  perhaps,  halfv.r.y  up,  to  carry  off  the  v;ater. 
Springs  are  frequently  encountered  in  deep  trenches,  and  may  cause 
trouble.  The  worst  cases  occur  at  the  junction  of  strata  of  compact  clay  \vith 
gravel,  or  coarse  v.atcr  bearing  sand.  In  clay  or  find, sandy  soil,  precaution 
should  be  taken  to  plug  or  stop  springs  or  permanently  drain  them,  otherwise  the 
flowing  water  may  eventually  \vash  awey  the  fiioer  materials  and  undermine  the 
foundation,  \7here  complete  drainage  is  impracticable,  springs  frequently  are  very 
ti  ouTblesome  during  construction,  impeding  the  workmen  and,  where  concrete  or 
.nasonry  is  used,  washing  out  the  cement  bc-forc  it  has  had  time  to  set.  If  the 
water  Cc.n  b  e  gathered  into  one  stream,  it  :••&.-»  bo  led  av.ay  by  a  pipe,  permanently 
jmbedded  in  the  foundation.  In  firm  material,  such  as  rock,  hardpan,  or  compact 
clay,  springs  may  be  plugged  by  masses  of  hydraulic  cement1  mortar.  In  the  con- 
struction of  dams,  or  retaining  \7ells,  vent  holes  sometimes  crc  built  in  the 
masonry  and  the  water  allov;ed  to  flov;  freolv  until  the  structure  has  been  built 
to  such  a  height  that  the  water  roe.chos  its  natural  level.  At  times  masonry  is 
laid  on  heavy  tarpaulins,  cove-red  with  pitch.,  or  other  waterproof  material,  to 
prevent  the  sashing  away  of  the  cement.  In  extreme  cases,  springs  or  the  entire 
foundation 'site  may  have  to  bo  surrounded  with  tight  sheet  piling  to  exclude  the 
water  from  the  space  enclosing  construction. 

Sand  Pilo.g_ 

The  bearing  pov/or  of  compressible  soils  e  en  be   increased  by  method's 
which  compact   the  material  as  veil  as   by  draina-je,  thereby  increasing  the   support 
ii:g  power  and  materially  decreasing  the  liability  to  settlement.    Soils  can  be 
co-pacted  by  sand  piles  and  "by  stock  ramming,   iieither  of  these    methods   is  common, 
altho'ugh  they  have' been  used  advantage  ously  ir  so  no   cases.        The   sand  pile  is 

formed  by  driving  an  ordinary  timber  pile  into -c Jo  soil  to  the  desired  distence, 
chen  quickly  withdrawing  it  and  immediately  filling  tl:.e  jolo  wit>  sharp  sand.  The 
density  of  the  soil  is  increased  if  the  sand  is  pk-.ced  in  the  I  ole  in  layers  and 


44 

rscmed;  because  seme  of  the  send  vdll  be  forced  laterally  into  the  surrounding 
mat-rial,  thus  largely  augmenting  its  supporting  pa; or.  The  increased  solidity 
secured  vill  depend  upon  the  number  of  sand  piles  driven,  the  piles  being  more 
numerous  as  the  original  compactness  of  the  rate-rial  is  less.  The  piles  may  be 
placed  from  2  1/2  to  6  or  8  ft.  apart  on  centers.  If  too  many  sand  piles  are 

driven  the  ground,  is  liable-  to  hea.ve» 

%  > 

STOC::-:  RU/DIIES 

The  process   of  stools  ramming  consists  ii;   forcing  clay  or  clayey 
natc-rial  into  the   interior   of  the  yielding   nass   of  earth  v/hich  is  c".  o signed  to 
carry  the    structure.  ::  pipe  2  to  3   or  4  inches   in  diameter  may  b  o  driven  to  any 
required  depth  from  5  or  6  to  25  or  30   ft.    into  the    foundation  bed.  An  iron  or 
stoel  rod  closely  but  freely  fitting  its  ':>oro  is  used  as  a  ranncr  from  a  frame 
erected  over  the  uppc:    end  or    uouth  of  the-  pipe.  Balls  or  cartridges  of  the  clay 

* 

ar  clayey  matorirl  made   from  6  to   12  or  15  inches  in  length  are  tlx-n  put   into   the 
pipe  and  rammed  into   the  material  adjacent  to  its   lav  or  ^nd.  '.hen  a  sufficient 

quantity  lias  boon  thus   forced  into  t~...e   surrounding  .ur.ss.,  the  pipe   isv:  ithdrav/n 

. 
from  2  to  4   or  5  ft.   and.  the  process  repeated.   In  this  r.ianncr  the  required  amount 

of  sfcbck  may  be  ramrod  into   the   foundation  bed  at   such  depths  and  elevations  as 

are 
vill  produce  the  desired  degree   of  compactnesc.    If  sane   and  gravel   :  ::nixcd  v;ith 

the   clayey  stock  to   b..    ranged,    it  must   be   in  sufficient ly  moderate  amounts  not  to 
jam  or  choke   in  the  pipe.  This  process,    like  all  similar  operations,  vrill  d  opend 
for   its  extent  and    frequency  of  applicrtion  to  any  giv..n  found.ation  bod,   upon  tho 
judgment   of  the    engineer   in  charge   of  the  v;ork. 

SAIflD  IAYERS 

Soft  and  yielding  material    frequently  maybe  very  much  improved  in  its 
bear  ing -capacity  by  an  cjccavatio:    £vom  1   or  2  to  even  §  or  6   ft.  beloi,'  the   bottom 
of.  the  proposed  foundation,   and  r-filling  vith  cloa.  ,   shcjrp  send.  The  send,  should. 

be  placed  in  layers,  moistoncd  and  relied    so  as  to   be   forced   into  tho    surface   of 

-i 

tho   surrounding  material  and  cxipactcd.   The  foundation  pressure  which  acts  upon 

ouch  a  base  or   bed  v/ill  be   transmitted  in  lateral  directions  so  as  to   increase 


45 

/ 

very  considerably  the  aroa  over  vhipJi  tlio  presaire   Is  ultiinatcly  distributed. 

It   is   sonctinos  necessary  to    found,  structures  like   railroad  embankments 

upon  semi-liquid  soils    in  marshy  or  sva;npy  land,   at   levels  so    lov:  that  drainage 

/ 

is»  i  .practicable.  In  such  cases  great  improvement  results  by  dumping  in  sand,  gravel 
and  broken  rock,  allowing  tho  materials  to  fine  their  ov.n  levels  and  distribution 
by  settling  i.:  tho  :nud.  This  method  >£  s  boon  used  extensively  for  some  of  the 
.larger  structures  on  tho  Panama  Canal?  also  v;hero  California  Railroads  have  been 
built  across  lovlying  laarshus.  Railroad  embankments,  aqueducts  and  outfall  sev;eis 
sometimes  have  been  supported;  i:.  svr..;ps,  on  fascines  or  mattresses  of  brush  and 
lo^s.  The  bearing  povrer  ov  even  a  fairly  solid  soil  usmally  v:ill  be  increased  by 
spreading  upon  its  surface  a  layer  of  sand  or  gravel* 

TEST  IKS  TEE  B^iaiEG  PCTSS  .OF  SOILS. 


of 
Direct  tests  of  tha  bearing  -per:  or  soils  are  made  frequently,  especially 

in  nc-v;  and  untried  Ix  at  ions,  before  completing  tlio  design  of  foundeticms  for 

important  structures  .•  Tho  tests  should  bo  conducted,  if  practicable,  at  the  bottom. 

% 

of  trenches,   excavated  to  the  sc.r.a  depth  as   is   proposed,  for  tlw  actual   foundctions, 
and  vith  tho  soil  in  its  nonnal  condition.  The   test  load  should   cover  as  large 
an  area  as  possible    (one  £q.    ft.    is  frequently  used).  The  a  at  hod  commonly 
anploycrV  is  to  dig  a  laolo  1  to  2  ft.    squaic-,  several  fo.t   deep,  to'placo   in   it 
a  heavy  timber  post,   12  by  12  rnches,    in  cross  section,   5'*.o  10  ft.    long.  Tho 
post    is  supportoc  by  gay  ropes,  a   strong  platform  built  on  top  of  it,   to  be 
loaded  vith  pigiron,   rails.,    or  sacks  of  cement.  A  number  of  stakes  should  bo 
driven  in  the   immediate  visit?  it  y  and  their  elevations  carefully  determined.   The 
tests   should  bo  continued  for    several  days   or  \vcoks  ,    rnd  accurate  observations 
made  of  its   sottle.:iont,  also   of  any  changes   in  the  level  of  the   surround.  ing  soil. 
If  earth  saves   form  nerr  the   trenches,    it   is  an  indication  that  tHe  soil  is 
disintegrating  or  unstable.   Frequently,  t\vo  posts  arc  sot,    connected  by  a  saddle. 
or   four  posts,   supporting  a  hoavy  table  3  to  5  ft.   square.   Tho  soil  sometimes 
is  lce-ot  'moist  c.rd  the  Iced   shaken  in  order   to  :;ivo  tr.3  i/orst  possible  condioixs. 


46 

The  foundations   for  the  St.   Paul  building  in  Nev;  York   (Eng. Record,  May  2,1896) 
were  tested  with  a"  single  post   loaded  to  6.5  tons  per  sq.    ft.    The   load  v/as  shaken 
?nd water  poured  into   the   trench   for  sovarr.1  v.eeks,   the  final  settlement  being 
19/32  of  an  inch.   The  foundations   for  the  largest  chimney   in  the  world  at  Great 
Falls,  Montana   (Eng.   Record,   Nov. 23, 1903)  were  tested  with  four  cast   iron  plates 

2  ft.    square;  200,000  Ib.    of  steel  rails,    equal  to  a  pressure   of  6.5  tons  per 

sq.   ft.  were  required  to  er.usc  a  settlement.   This   chimney  is  506  ft.   high,  weighs 
18,000  tons;   the  diamater  varying  from  50  to  80  ft.   With  a  wind  allowance  of 
33  1/3  Ib.  per   sq.    ft.   corresponding  to  a  velocity  of  135  miles  per  hour,    the 
•narimum  pressure   on  the  .foundation  bod,    of  uniform  shale   22.5  ft.  below  the 
surface,    is  4.83  tons  per  sq.   ft. 

In  August  1907  a  test  v/as  made   in  Oakland,  California,   by  the  Board  of 
Public  \7orks,    for  a  foundation  site  to     carry  a  fiv,.   story,   Class  B,  reinforced 
concrete  building.   The  soil  under  tha  proposed  footings  consists   of  a  mixture  of 
clay  and   sand,  about    in  the  proportion  of  7  to  3.   The  subsoil  had  been  excavated 
to  a  depth  of  10    ft,   over  the  entire  lot  area  of  10,000  so.    ft.    ;    the   footing  bed 
at  10   ft.   r.epth  had  been  graded  and  the  loose  soil  made   firm  and  compact  by 
frcruent  wotting.    It  was  questioned  v.'hethor   this    soil  could  carry  5   tons  per  sq. 
ft.  A  large  sugar  pine   stick,    12"  x  12"  x  10'  was    supported  on  tvo  sides  by 
scantling.  After  tho   loo&e  surface  material  had  boon   scrap;'."    away  to  a  depth  of 

3  inches' the  bo'ttom  of  the-  ^inc  stick  wrs   allow  ,d  to  rest   on  the   soil     The   load 

t 

acmsistoo.  of  old    stool  rails  and  barrels   of  ce..icnt.   The.  cement  was  rolled  upon  the 
jlatform  with  much  shock.  A 'record  of  tho   tost    is  as   follows:      (see  page  47) 

For  a  total   load  of   31,000   Ib.    or  15.5  tons  per  *.  .    ft.    representing  a 
?actor  of  safety  of  5,   tho   total   settlement  was  0.85  inches-,  whicl.   increased  to 
A.87   inches  in  48  hours.    It  v/as  concluded  that  "the  soil  v/as  amply  safe  to   carry 
'-•ho   footings  to  be   installed  and  tho  structural  loads  thereon". 


.-       .    ': 


47 


Date 

Timo      Load  in  Ibs. 
per  sq.ft. 

Depression 
inches 

Aug.  12,  1909 

2:30  p.m. 

0 

0.0 

12 

3:30  p.  3. 

2175 

0.0 

12 

4:00  p.m.. 

4256 

0.0 

12 

4:15  p.m. 

6426 

0.1 

12 

4:30'  p.  .-;. 

8501 

0.15 

12 

5:00  p.m. 

10576 

0.2 

15 

5:00  p.'.a. 

10576 

0.2 

16 

8:30  a.m. 

12651 

0.25 

17 

3:30  a.m. 

31000 

0.85  . 

17 

5:00  p.m. 

31000 

0.85 

19 

8:30  a.m. 

31000 

0.67 

In  Engineering  News -Record,  Vol.  89,  July  13, 1922, p.  73,  is  described 
a  continuous  mat  foundation  for  a  22  story  building,  the  Standard  041  Building, 
San  Francisco,  founded1  on  an  inverted  floor  of  reinforced  concrete  3  ft.  thick, 
reinforced  by  girder  ribs  b etwocn  column  footings.  The  article  illustrates  the 
test  apparatus  used  to  determine  the  bearing  quality  of  the  soil,  Bush  and  Sansome 
St.  Cf.  also  Proc.  Am.  Soc.  C,£.  ,  ifarch  1922,  p.  523,  for  a  more  elaborate 
discussion. 

PRESSURES  ON  FOUNDATION.  BEDS 

Abnormal  Pr e s sur o .   The  abnormal  pressure  on  a  foundation  bed  produced 
by  a  structure; ,  is  the  pros  sur  ^  which  is  in  excess  cf  that  v.'hich  existed  there 
before  any  excavation  v/as  .?ade.It  is  equal  to  the  total  final  load  on  the  found- 
ation bed,  minus  the  original  weight  on  the  bed  caused  by  the  pressure  of  tho 
earth,  sand,  rock,  mud,  water,  originally  above  it. 

EXAMPLES  OF  PRESSURES  ON  FOUj^mTIONS.  AND 
FOUNDATION  BEDS  IN  LAH?H  AN p_  SAHD 

Example  Tons  per  sq.ft, 

Pressure  on  concrete  and  granite  masonry,  Brooklyn  Bridge  26 

.abnormal  pressure  on  firm  sane,  in  ba~s  and  estuaries  5.0  to  5.6 

.Abnormal  pressure  on  firm  sand  and  sandy  gravel  616  to  7.8 

Vbnormal  pressure  on  firm  shale  and  gravel  6.7  to  9.0 

' bnormal  pressure  on  compact  gravel   .  7.8  tc  10.1 
.Washington  .Monument: 

1  =  Excluding  wind,  average  pressure  on  base  .     5.67 

2.  Average  of  same  under  concrete  base,  upon  sandy  and  gravelly 

ground  6.5 

3,  Maximum  pressure  possible  v;ith  wind  9.0 
bunker  Hill  Monument,  hard  sand  and  gravel  5.5 

lurch  Tower,   Fifth  Avo.   and  27th  St.,   New  York  City,   hr.rdpan  7.0 


48 


Bridge  over  Ohio  River,  Cairo,  111.,  piers  50  ft.  into  sand: 

Max.  abnormal  pressure  under  piers  4.0 

Mas.  v:hen  allowing  for  skin  friction  3.0 

Proposed  Korth  River  Bridge;  abnormal  pressure  on  send: 

Promoter  proposed  7.16 

Finally  limited  to  5.0 

Hawksburg  Bridge,  Mew  South  V/ales;  water  70  ft.  deep,  foundation 

bed  162  ft.  belov;  water  line;  8  ft.  into  sand,  abnormal  pressure      5.7 
Summary,  pressures  upon  earth  and  sand 

Average  for  good  deep  foundations  5.0 

Average  for  good  shallow  foundations  3.0 

The  above  are  all  for  deep  foundations  upon  sand. ,  gravel  or  granular 
deposits.  Belov,-  are  average  values  for  light,  shallow  foundations  in  clay,  sand 
and  earth. 


T7ell  drained  clay,  always  practically  drgr 
Clay>  moderately  dry 

Clay,  soft,  moistened  (Chicago  conditions  ) 

Coarse  sand  or  gravel,  in  strata,  undisturbed  and  well  bonded 
Ordinary  sand,  thoroughly  compacted,  bonded,  and  well  held 
in  place 


Tons,  p.  sq.ft 
4.0  to  6.0 
2.0  to  4.0 
1.0  to  2.0 
6.0  to  S.O 


2.0  to  4.0 

The  pressures  on  a  number  of  deep  foundations,    in  tons  per  sq.    ft. 
of  2000  Ib.  as  'determined  or  listed  by  E.  L.Corthell,  are  as   follows: 


Material 
1 

. 

Pressure,   tons  pe 

c   sq.    ft. 

No.    of 
examples      | 

rain  .    ' 

max.          !      avg. 

!     Fine  sand                                     \   2.25       |     5.8 

4.5                             10 

Coarse  sand  and  gravel          j   2.4 

7.75 

5.1 

33 

Sand  and  clay 

2.5 

8.5 

4.9 

10 

Alluvium  ani  silt 

1.5 

6.2 

2.9 

7 

Eard  clay 

2.0         !     8.0 

5.08 

16 

Hardpan                                             3.0         ;  12.0 

8.7           :                     6 

See  reference  No.   7  at  the  close  of  this    chapter. 

Corthell  further  finds  the  following  frictionr.1  resistances  between 
pier  sides  and.  foundation  materials.   For   steel  cylinder  piers,  thoyaiethe 
least  for  .nud,   the  mofet   for  gravel.  For  masonry  piers  the  figures  are  lov/est   for 
sand,  and  gravel,   greatest   for  sane:  and  clay. 


Fractional  Resistance,    Ibs.  'oor   sq.ft. 

Ho.   of  Examples 

l.lin. 

1      I/lax,                i        -kvoraso 

300 
300 

205 

i 

1500 
1000 
450 

540 
522 
270 

10  cylinder  piers 
23  r.iasonry  piers 
5  walls,   quays,   etc. 

For  average  values  of  the  coefficient  of  skin  friction,   Corthell   s 


sheet  iron  on  sand 
sawed  lumber  on  sand 
masonry  on  sand 


0.4 

0.65 

0.65 


49 

1.0.  Baker  in  his  Treatise  on  Masone-y  Construction,  10th  ed.  ,  1S09  ; 
p.  464,  gives  r,  more  o:Lhaustive  table  of  values  for  coefficients  of  si:  in  friction 
Seo  also  Tablo  59,  p«  342,  on  safo  boar  ins  power  of  soils.  Examine  Tables  1,2,3, 
by  A.C.Alvarez,  on  properties  of  materials. 

PiY;  FOUNDATION  SOILS:  TEEIH  SUPPORTIK3  CAPACITY 


1.  Any  material  vrhicl:  can  be  called  rock,  vhen  its  bod  is  properly 
cleaned  and  prepared  foi  the  foundation,  vill  bear  safely  any  stricture  liable 
to  b  e  placed  upon  it. 

2.  Boulders  and   gravel,   usually  are  able   to  support  any  ordinary 
structure,   especially  when  they  arc  cemented  into  hardpan  by  mixing  v.lth  small 
quantities  of  sand  and   clgy  or  earth. 

3.  Ordinary  (siliooous)    sand  vill  bear  safely  heavy  loads  if  the    sand 
is  properly  confined;   but  great  care  must  bo   taken  to  prevent    it   from  spreading 
laterally;   also,   to  prevent  scour   from  the  action  of  running,    or  even  percolating 
v/ater. 

4.  Clc.-y  makes  a  satisfactory/  foundation  bed  when  it   is  kept  dry. 
Particular  care  should   be  taken  to  prevent  clay  from  being  alternately  v;ot  and 
dry;  a  Iso  to   carry   foundation  trenches  v;cll  b  elov;  the   frost  line, 

5.  Good  foundations    can  be  constructed  on  sediment  soils   or   loam  if  the 
•material   is  homogeneous  throughout  tr..e   entire  rrea  undoi  lying  each  structure; 
and  v.cer   in  addi.ion  the  design  provides  ane^ual  intensity  of  load  under  all 
footings.    Some  settlement  I/ill  occur,   but   it  v.lll  not  bo  particularly  injurious 
if  Si7r.ll  in  amount,  ard  uniform  for  each  structure. 

6.  By  special  treatment  ,,  quicksand  or  semi-liouid  marshy  soil  can 
support  moderate  .lor,  ds.   iiuch  of   its'boaring     pov/er  depends  on  tv,e  principles   of 
flotation  and  skin  friction;  hence  the   foundations    should  be   sunk  as  deep  a  s 
possible.      It  may  be  necessary  to  employ  unusual    processes,    such  as   freezing  or 
cement  grouting,   but   o  :on  excavations  can  bo    tadCv 

7o   Except    for  a  structure   founded  on  solid  rock.,   the  base   bed  or 
footing  should  be  spread  sufficiently  to  keep  the  foundation  pressures  per  sq. 
ft.  t.'ithin  allov.rble   safe   limits   for  soil  bearing  capacity;   the    foundation  should 
bo  carried  bolovtho    frost  line,    and  in  soft  materirl,   as  much  deeper  as  prac- 
ticable.  For  substructures  resting  on  rock  or  hard.pan  c:  ro  should  be   exercised 
to   limit  pressures  on  foundation  b-^ds  so  -chat  they  do  not   exceed  safe  compress-  ' 
ivc  stresses  for  the  materials  used  in  the  footings 

.  .       <  t 

ADDITIONAL  REFERENCES 
FOUNDATION  SOILS  AND 


1.  A  Practical  Treatise  on  Foundations;  V/MLPatton;   art   1,  pp.   1-^ 

2.  A  Trortisc  on  Liasonry  Construction;    I.O.Balcer,   Part   III,  pp.   333-347 

•3.  The  Foundations   of  the  Kcv;  Caiitol  at  Albany,  W,  J.ilcAlpine;   Trrns,   Am.   Soc. 

C.E.  ,   Vol.    11,   p.  287,   1873. 
I..  Description  of  the  Iron  Viaducts   erected  across  the  Tidrl  Estuaries  of  t:.e 

k  Rivers  Leven  and  Kent,    in  Moreccmbe  Bc.-j,    for  the  Ulver  stone  and  Lr.ncaster 

Ry>  ;   by  Jrmes  Brunlcos,   Proc.   Inst     of  Civ.   Engineers,  Vol.    17,  p.  442, 
1858, 


50. 

5.  Cleeman's  E, R.   Practice,  pp.   193-104., 

6.  Professional  Papers,  Eayal  Engrs.   Vol.   20,  p.   ISO,   Quicksand  Foundations. 

7.  Allov/able  Pressures  on  Docp  Foundations;  L,L.Corthell;   see  particularly  p. 37 

for  58  references    from  Ermine or ing  Index,    1896-1900. 

8.  Architects'   and  Builders'   Pocket  book,   F.L.Xidder,  Chap.    II  >    pp. 155-146, 

9.  The  Station  B  Chimney  of  the  17  av;  York  Steam  Co.  „  Chas.   E.Emory;   .Trans.  Am.   Sx  . 

C.E. ,   Vol.    14,   p. 182,   1885. 

10.  The  Y/eight  on  Foundations  of  Buildings;  H.Leonard;  Engineering,  Vol.  20,  J.103; 

1875. 

11.  Proc.    Inst.  C.3.   Great  Britain,  Vol.   CLZV,   1905-6;   Part  3, 

12.  fi  conrpositc   sr.nd  and   rode   foundation;  :,lunicr3al  Bldg.    ,  Net;  York  City;  Eng. 

Nev/s,  Vol.    63,   Jan. 6, 1910,  p. 24;  also  Vol.    64.   Nov.    17, 1910, p. 523 

-13.    Hardpan.'"  and  other  Soil     Tests;  by  J.M, Jensen,   Eng.   Kev/s,   Vol.    69,  i-iarch  6,1913, 
p.  460. 

14.  Testing  Rock  Bearing  by  Leverage  Load  ing 'Machine ;   Eng.   News -Re-cord,   Vol.    85, 

Aug.    26,1920,   p.   417 

15.  Foundation  Tests   for  Nebraska  State  Capitol;   Eng.   Hev/s -Record,  Vol.    85     Oct.  12., 

1922,   p.    606. 

16.  Tests  of  the  Bearing  Capacity  of  Soil;    St.   Paul  Building;  Eng.   li'ovvs ,   Vol.    35, 

p.   310 

PROBLEMS 

1.  State  different  methods   for  consolidating  soft  and  compressible  soils  to 
increase  their  bearing  capacity  for  shallot?  foundations.    Illustrate  where  necessary. 

2.  Give  range   in  each  ease   of  numerical   values   for  sr.fo  bearing  pov/er  of 
various  foundrti on  soils   from  took  to  the  most  treacherous  types. 

3.  The  greatest  slops  of  an  earthy  hillside   3s    24*.    If  the  angle  of  repose 
is  32*  ,   compute  by  Ranlcino's   formulas   the  passive   intensity  at  a  depth  of  34*. 
7/hr.t   is   the  abutting  intensity?  Compute  by  the  s  arae   theory  the  position,    c'irectim 
and  amount  of  the  total  passr-ve  and  abutting  thrusts  respectively  exerted  against 
a  vortical  surface  3'   V  by  1'   H,   38'.  belov/  the   surface.    Submit  a   scale   diagram, 
Cf.  KG t churn,  I/alls,  'Bins  and  Grain  Elevators,   Chap.    I,  particularly  oqs.   7  and  8. 

4.  In  v:et  sand  v;hosc  top  surface   is  horizontal,  \vhat  vertical  pressure   everted 
upon  a  foundrtion  bod  24'   belov.'  the    surface  v/ill  just  tend  to  heave  the  surrounding 
material? 

.     5.   Define  abnormal  pressure   for  a  foundation  bed.  Bivo  skin  friction  resistance 
for  tho  sides  Of  piles  and  caissons  s.unk  in  different  soils, 

6.  A  total  load  of  10.55  tons  rests  upon  a  16"  s.  16"   timber  usoc1  as  a  test 
piece  to  investigate   the  bearing 'capacity  of  a  given  soil.    'That   is   the  pressure   en 
the  soil   in  ;,',D'    i-f  the  load  is   central?     YThy  is    it   important  to  have  the  load 
central?     If  in  one  direction  the  load  is   eccentric  3  1/4",  compute  the  min.    and 
-:a::.  pressures  exerted  upon  tho   SD  il. 

7.  In  tho  throe  cases  given,  \vhat  pressure  may  be  allowed  untfor  a  contiguous 
;oncrot''    footing  \:  ich  supports  a  building  v;ith  brick  avails.   The    foundation  soil 
is    (a)   earth,    (b)  dry  sand,    (c)  hardpan.   Explain  th:   effect   (on  values  assigned) 
)f  depth  bclor;  the  surface-  of  the  ground. 


51. 

CHAPTER  ^ 


CLASSIFICATION  AND  KEQUIK2MENTS 
FOUNDATION  DLSIC-KS 


Classification. 


After  complete  explorations  and  soil  studies  have  boon  made  to  enable  the 
engineer  to   select  a  proper  scheme   of  foundation,    the  plans   for  the   substructure 
-nay  bo  olaborrtec".   Foundation  types  do  not  ad-nit   <5f  vary  distinct  classification. 
They  may  bo  grouped  as    follov/s: 

A.  According  to  the  Material  Upon  Which  they  Rest, 

1.  Foundations   immediately  on  rock 

2.  Foundations   on  hardpan,   confined  sand  or  dry  clgty 

3.  Earth  or  soil   foundations 

a.  ordinary  soils 

b.  compressible  soils 

c.  seal-liquid  soils 

B.  According  to  Type  of  Structure  Designed 

1.  Footings:-  timber;  offsets  of  nasonry  or  concrete;  timber 

grillages;  inverted  arches  of  brick,  masonry  or  concrete; 
steel  'Tillages  of  roiled  I  or  channel  beams  and1,  concrete, 
reinforced  concrete, 

2.  Shoot  piling:-  timber,  steel,  reinforced  concrete;  light 

and  heavy  sheet  piling- 

3.  Bearing  Pile  Foundations:  timbo, ,  reinforced  concrete,  metal 

4.  Coffer  dams 

5.  Upon  caissons 

6.  Pneumatic  caissons 

7.  Deep  v;cll  dredging 

8.  Combination  and  miscellaneous  foundations. 

In  v.'hat  follov/s,  this  classification,  so  far  as  feasible,  v/ill  be  observed. 
Foundations  usually  arc  sufficiently  complex  to  bo  included  uncer  tvo  or  mere 
of  these  headings.  Shoot  piling,  by  itself,  is  not  a  foundation,  but  may  be  a  voyy 
necessary  preliminary  part  v.'hich  makes  possible  excavation  in  soft  material  and 
then  protects  the  real  foundation  during  its  construction. 
Zoundat ion  Bco ui roraont s 

1.  SJicnevcr  possible  a  foundrtion  bed  should1,  bo  rough,  properly  stepped, 

% 

-nd  perpendicular  to  thv,  resultant  pressure  upon  it.  In  general,  like  a  masonry 
joint,  it  must  be  capable  of  v.lths tending  overturning.1  sliding  and  crushing.  To 
".void  tension  in  t>o  bed,  in  no  case  should1  'the  resulting  pressure  lie  outside  of 


52 

tho  middle    third,   Usually  the  slier-ring  strength  of    the    bed  is  neglected;   then  to 

0 

prohibit  sliding,  the  resultant  pressure  must  never  make  v/ith  the  normal  to  tho 
bod  an  angle  exceeding  the  angle  of  friction  for  tho  materials  of  the  bod. 

2.  A  foundation  bod  must  always  be  placed  safely  below  the  depth  to  which 
freezing  and  thawing  penetrate. 

3.  Always  e;:cludc  surface  wators  from  a  foundation  bod;  confine,  stop 
or  regulate  the  flow  of  underground  water. 

4.  Attempt  to  prepare  a  foundation  bed.  so  that  it  offers  a  uniform 
jaatorial;  that  is,  one  of  equal  bearing  capacity  and  equal  compressibility  for 
.the  entire  area  of  foundation  base, 

5.  Footings,  particularly  for  buildings,  and  especially  for  walls  vs. 
interior  columns  of  buildings,  should  bo  designed  of  such  dimensions  that  the 
foundation  bod  at  all  places  under  the  structure  is  subjected  to  tho  same  intensity 
tef  pressure,  otherwise,  even  with  equal  homogeneity  or  compressibility,  unequal 
fccttlomcnt  will  take-  pir.  cc. 

6.  For  complex  'footings,  the  resultant  lord  on  the-  bod  must  coincide 

. 'ith  the  center  of  gravity  of  tho  foundation  plan,  assuming  uniform  pressure  on 
t'-!.o  bod;  otherwise,  the  foundation  will  be  subjected  to  a  bending  couplo  and 
/."ill  tend  to  tilt  or  settle  unequally.  The  so-called  t.apezoidal  or  combined 
irb  footing  for  a  building  exhibits  a  si.nplc  example  of  the  application  of  this 
rinciplo;  where,  to  roruco  the  magnitude  of  the  pressure  intensity  on  the  bed, 
wall  and  an  interior  column,  unequally  leaded,  arc  jointly  supported  on  a 
ounce ting  slab, 

7.  Tho  main  t>arts  and  all  structural  details  or  joints  for  simple  or 

. 
.:pl cm' foundation  structures  must  be  designed  for  the  materials  used  and  tho" 

.zinu-.;  stresses  to  be  borne.  In  bridge  trusses s  building  grrmcs  and  other  similar 
scs,  the  probable  str.sscs  cm  bo  computed,  with  a  considerable  degree  of  accuracy- 
om  the  nature  of  substructure  designs,  thoy  arc  more  massive  than  steal  trussing 
LC:  --lees  it  more-  difficult  to  analyze  for  existing  strossos.  Usually  only 


53 

approximate  calculations  con    be  made.  A  sound  judgment  must  bo  exercised  in  fig- 
uring safe  dimensions;    for  example,    for  the  roof  beans,   side  rails,    side  v/all 
brackets,   and  cutting  edge  of  a  modern  structural   stool  pneumatic  caisson.    Simple 
methods  only  can  be  used  \vhon  stress  calculations  are  made  for  the   design  of  v;all 
timbers,    bracing  struts  and  anchorage  rods   in  a  typical  timber  cofferdr,.n.    Intoll- 
^igent  methods   for  analyses  nust  be  proposed,  safe  specification   for  v/orking 
stresses  written  and  sane    selections  .rsac'o   for   the  particular    naterisls   to  be 
employed  (whether  wood,   metal  or  :iasonry).In  one  case  vood  is  the  logical 
material,    in  another,    it   is   steel  or  reinforced  concrete. 

REFERENCES  -  SPECIFICATIONS 

'1.   General  Specifications    for  Foundations  ancl  Substructures  of  High-ay  Bridges; 
by  T.   Cooper,    1902. 

2.   General  Specifications  for  Bridge  Substructures;    oho  Osborn  Co. 

5.   Specifications   for  Ilasonry;  Appendix  3;  A  Treatise   on  Ilasonry  Construction;  by 
I. 0, Baker,    10th  od. ,   1909,  p.    729. 

4.  Sec  Appendices  -  Ordinary  Foundations,    by  C»    L.    Fov/lcr 

5.  See  Appendices   -  Subaqueous  Foundations,  and  Lnginooring  and  Buildirg 

Foundations;   by  C.   E.   Forolor. 

^m  • 

6.  Foundations  of  Bridges  anc! 'Buildings;   by  Jacob;-  &  Davis,   Chap.    IS;  references. 

7.  Design  of  Ilasonry  Structures  r.nd  Foundations;   by  C.C.".illia.rs. 

BROBLE.IS 

1,  State  the  seven  .or  more  important  requirements  which  should  bo  observed  in  the 

preparation  of  foundation  bids  rue.  the-  design  of  foundation  structures. 

2,  Name  tho  different  typos  of  foundation  structure  as  enumerated  in  Chap.  3. 

m  List  the  chief  groups  of  masonry  structures  discussed  in  the  texts  of 
references  3  to  7  inclusive. 


. 


'-;   '  '.     '• 

f.Jcii;".  .  •  .  -i  :  -• 


54 

CHAPTER  4 
DISTRIBUTION  OF  FOUNDATION  PRLStURES  -  SPREAD  FOOTINGS 

Unless  a  structure  is  founded  on  solic3  rock,  it  is  necessary  that  the 
foundation  have  an  area  sufficient  to  give  safe  unit  pressures  on  the  bed.  ,,iany 
soils,  in  any  event,  will  permit  of  slow  settlement,  which  may  not  be  particularly 

injurious  if  uniform  throughout  the  entire  s  true  ture.  In  order  to  secure  uniform 

** 

settlement  it   is  necessary,   if  the  underlying  material   is  homogemeous ,    to  design 

the   footings  for  various  parts  of  a  structure  so  that  the  pressure  on  the  bed  v/ill 
be  of  constant  intensity.    If  parts  of  a  foundation  bed  are  more  compressible 
than  others,    the    footing  should  be  so  d  esigned  that  the  unit  pressure  v/ill  b  e 
less  on  the  weaker  material. 

The  major  pressures  on    foundation  bed's  are  produced  by  the  dead 
weight   of  the   sub-  and  super-structure  plus  the   live  load  which  they  are 
designed  to  carry,  all  acting  vertically,  ilany  s  tructures ,   in  addition,  are 
subjected' to  various  lateral  forces;   applied  horizontally  or  inclined  at  any 
angle.   For  fcall  buildings,    chimneys,    towers  or  monuments',  horizontal  wind  pres- 
sures are   important.   For  slender  bridge  piers,    it  is  necessary  to   consider 
besides  wind  such   forces  as   the  dynamic  pressure    from  running  water,   and 
pressure  from  drift  rood  or  ice.    In  some  cases  also    tractive  or  centrifugal 
forces c ausod  by  moving  loads  on  the  superstructure  may  not  bo  negligible. 
Foundations    for  docks  or  quay  walls  should b e  designed  to  withstand   impact    from 
v/avesand  moving  ships.    Foundations   for  arched  b  ridges  and  retaining  walls 
must  bo  designed  to  resist   lateral  thrusts.    In  archos  and  suspension  bridges 
it   is    important  to  consider  temperatuie   stresses  arising  in   the   superstructure. 
For  anchorage  piers  of  cantilever  and  suspension  spans,    there  may b o  large 
uplift  forces. 

The  vortical  loads  usually  are  much  larger  than  the  inclined  or 
horizontal  ones;   they  frequently  cause  the  only   foundation  -pressures  requiring  - 
consideration.  A     careful  analysis    for    foundation  s tability  of   a  structure 


55 

should  always  be  made,  considering  the  dead  loads  of  sub-and  superstructure 
with  all  possible  combinations  of  live  loading,   lateral   forces  and  uplifts.    The 

m  "\ 

magnitude,  line  of  action  and  point  of  application  of  the  resultant  force  on 
each  foundation  footing  should  be  determined  before  accepting  the  superstructure 
design.  Similar  calculations  should  be  made  for  joints  at  other  levels  above 

the  bed;  particularly  in  tall  piers.  The r  esultant  force,  in  most  cases,  is 
not  fixed  either  in  position  or  amount,  because  of  the  constant  variation  of 
live  loads  and  lateral  pressures, 

In  buildings  the  dead  weight  of  the  structure  can  be  .computed  from 

the  cubical  contents  and  the  known  weights  per  cu.  ft.  of  materials.  The  min- 
i 

imum  live  load  for  which  a  building  should  be  designed  is  fixed  by  the  specif  i- 

Bridges  r.re^  usually  designed  for  s.  series  of  wheel  concentrations 
cations i^which  represent  more  or  less  closely  the  loads  brought  on  the  Structure 

by  moving  trains,  road  rollers  or  trolley  cars.  Buildings  and  highway  bridges 
are  designed  for  a  certain  minimum  specified  live  load  "per  sq.  ft.  of  floor 
surface. 

The  following  table  taken  from  Baker's  Treatise  on  Masonry  Con- 
struction, od.  1909,  p.  348,  gives/unit  weights  of  masonry.  Handbooks  like 
Trautwine,  Kidder  and  Cambria  offer  more  elaborate,  specialized  tables  for 
masonry,  building  details,  weights  of  roofs  and  floors.  Consult  Kidder,  od.  1908, 
p.  1343. 

WEIGHT  OF  MASONRY 
Kind  of  Ursonry  Ugt.  in  Ibs.  per  cu.ft. 

Brickwork,  prossad  brick,  thin  joints 

Brickwork,  ordinary  quality 

-Brickwork,  soft  brick,  thick  joints 

Concrete,  1  cement,  3  sand  and  6  broken  stone 

Oranite,  6%  more  than  the  corresponding  limestone 

Limestone,  ashlar ;  largest  blocks  and  thinnest  joints        160 

Limestone,  ashlar,  12"  to  20"  courses  and  3/8"  to  1  1/2"  joints,  165 

Limestone,  squared  stone 

Limestone,  rubble,  best  14° 

Limestone,  rubble,  rough 

Sandstone,  14$  less  than  the  corresponding  limestone 


'£>.: 


56 

ADDITIONAL  QUANTITIES 

Typical  Structure  Ugt.  in  ftl>s.per._sg.  ft . 

Suspended  ceilings  (metal  lath  and  plaster)  '  10 

Ordinary  lathing  and  plastering  10 

Floors  for  dwellings  (usual  wood  jojst  construction)  10  to  30 

Floors  for  public  buildings  (higher  figures  ere  for  sto*>l  &  concrete,  45  to  100 

Floors  for  warehouses  80  to  120 

Shingle  roof  10 

Slate  or  corrugated  iron  roof  25  to  30 

Consult  Ketchup,  Steel  Mill  Buildings,  Pert  I,  Loads,  pp.  5-21; 
Also  Ricker,  Design  and  Construction  of  Eoofs,  Chap.  3,  pp.  22-25. 

The  minimum  live  loads  for  which  buildings  can  be  designed  will  vary 
in  different  localities  and  for  different  types  of  buildings.  The  Cambria  Steel 
Handbook,  ed.  1919,  p.  328,  gives  a  su.n.iary  of  floor  loads  prescribed  by  the 
Ordinances  of  thirty- one  American  Cities.  The  following  table  is  compile^  frcm 
Sec.  54,  ed.  1921,  San  Francisco  Building  Code: 

LIVE  LOADS  FOB  BUILDINGS 
Kind  of  Building  Live  load,lbs.  per  sq.ft 

1^  Dwellings,  office  floors,  apartment  houses,  tenement  houses., 

hotels,  hospitals  40 

2.  School  rooms  and  theatres  with  fixed  desks  and  seats,  stables 

and  carriage  houses  75 

3.  Garages,  automobile  salesrooms,  light  machine  shops  and 

department  stores  100 

4.  Halls  of  public  assemblages,  without  fixed  seats,  hells  of 

schools ,  theatres  and  hospitals,  ordinary  stores^and 

floors  of  light  manufactories,  warehouses  for  light 

storage  as  furniture  or  other  bulky  materials  125 

5.  Stores  -frith  heavy  loads,  stack  rooms  of  libraries,  warehouses, 

ordinary  manufactories 

6.  All  sidewalks 

7.  Roofs,  pitch  less  than  20°,   live  load  per  sq.    ft.-  horizontal 

projection 

8.  Roofs,  pitch  greater  than  20°,   live  load  per  sq.    ft.   horizontal 

projection 

See  also  Sec.   57  for  allowed  foundation  pressures;   "Soils  carrying 
foundations  shall  not  be  leaded  more  than  the   following  number  of  tons  par  sq. 
ft. :   soft  clay  =  1,    sand  and  c  lay  mixed  =  2,   firm  dry  clay  =  3,  hard  clay  =  4, 
loam  Or  fine  dry  sand  =  3,   compact  sand  =  4,  coarse  gravel  =  6,    shale  rock 
hard  rock  =  20.   Seo  also   Sec.    58  for  allowed  unit   loads   on  masonry.  Consult 
Cambria,  p.   338,   1919  edition. 


• 


57 

CENTER  OF  T/EI3HT   VERSUS   CENTER  OF  FIGURE  FOB  BUILDING  FOOTINGS. 
In  general,   the  most  important  guiding  principle   for  the  design  of 
foundation  footings   is   to  make  the  center  of  pressure  or  weight  coincide  as 
nearly  as  possible  with  the  center  of  area   of  the  base.   Footings   for  different 
parts  of  a  structure   should   be  proportioned  to  give  the  same  unit  pressure  on 
the  soil.    In  designing  continuous  footings   for  t  he  walls   of  buildings  on  homo- 
geneous ground,    the    footing  widths  should  vary  directly  with  t  he  weight  on  the 
wall.    If  a  heavy  exterior  wall,   WJL    (fig.    10)   is  rigidly  connected  to  a  light 
cross  wall,  V/g,  and  their   footings  are  of  the  same  width,   there  is  a  tendency 
for     the  inner  wall  to  crack.   Suppose  that  in  plan  10A,  the  line  of  action  for 
the  weight  on  the  walls  is   in  the  position  indicated  by  the  arrows,  A,  while 
the  upward  pressure  B  from  the   foundation  bod,    equal  in  amount  to  the  weight   of 

• 

A  but  opposite  in  direction,  has  its  point  of  application  at  B;  then  the  forces 
A  and  B  are  not  coincident.  The  foundation  should  bo  designed  with  a  narrower 
footing  under  the  cross  wall,  as  shown  in  the  plan  10B,  so  that  the  upward 
pressure  is  in t  he  position  indicated  by  the  arrow  C,  slightly  outside  the 
resultant  weight  A.  This  gives  a  tendency  to  the  outer  walls  to  incline  inward, 
a  movement  usually  prevented  by  the  interior  construction  of  walls,  W2,  floors, 

and  roof. 

If  a  portion  of  a  wall  is  omitted,  and  thus  its  weight  per  lineal 
foot  of  length  is d ecreased  because  of w indow,  door°other  exterior  openings, 
the  widths  of  the  footings,  fig.  11,  should  be  varied  to  make  the  unit  foundation 
pressure  uniform.  Outward  inclinations  for  walls  can  bo  counteracted  only  by 
anchors  or  tie  rods,  by  the  bond  of  the  masonry  or  by  masonry  buttresses.  Little 
reliatoo,- should  be  placed  on  more  walls  of  thin  masonry.  If  it  is  necessary  to 
design  a  footing  which  tends  to  produce  outward  inclinations,  a  masonry  or 
brick  building  should  bo  tied  carefully  together  w  ith  s  teel  r  enforcement  and 
joist  anchors,  especially  above  openings,  or  at  the  junctures  of  walls.  In 
general,  when  a  continuous  footing  is  built,  it  should  be  designed  so  that  the 


198    «W 

eBO?ft9? 


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srf; 


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, 

i.    .   .  -    'jJeo^t 

i  •      J          /&fr   £  ' 


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58 

center  of  loading,,  for  t he  various  portions,  falls  a  little  inside  the  center 
of  the  base  .areas.  At  Chicago,  the  omission  of  2%  of  the  weight,  by  window  or 
other  openings,  together  with  failure  to  decrease,  correspondingly,  t he  width 
of  the  foundation  footings,  in  numerous  cas'os  has  caused  unsightly  cracks. 

Consult  Freitagj;  Architectural  Engineering,  Chap.  5,  exterior  vails 
Piers,  pp.  144-166;  also  International  Correspondence  School  -  Structural 
Engineering  Course,  Statics  of  I/Iasonry,  Part  2,  pp.  1-89.   Eoad  in  the  San 
Francisco  Ordinance,  Part  9,  Special  -provisions  relating  to  Class  C  Buildings; 
Section  133,  which  discusses  the  thicknesses  allowed  for  walls  of  increasing 
heights. 

The  following  table  for  vr.ll  thickness  is  taken  from  the  1909  od. 
of  the  Building  Laws  of  the  City  of  Oakland.  Section  131,  -  "Exterior,  party, 
division  and  bearing  walls  of  brick,  except  as  provided  for  in  sections  128, 
129,  130  and  139,  shall  be  built  of  thickness  given  in  the  following  table. 
Division  walls  carrying  no  weight  may  be  four  inches  less  in  thickness  through- 
out, provided  however  that  one  Story  buildings  not  ovc-r  twelve  foot  higl'..  v;hcn 
used  for  storage  or  manufacturing  purposes,  may  bo  enclosed  with  brick  walls 
eight  inches  thick". 

Stories 


Building 
Height 

Basement  wall  ; 
thickness    ' 

First 
18  ft. 

i  Second 
!  31  ft 

•Third 
,'  44  ft. 

Fourth  1 
57  ft.; 

Fifth 
70  ft. 

Sixth 
83  ft 

i  Seventh 
i   95  ft 

(story) 

(Indie's) 

1 

1 

i 

1 

1 

1 

17 

13 

i 

" 

- 

- 

- 

i   ~   i 

;   2 

17 

17 

13 

i   ~ 

- 

- 

i   -   1 

3 

21 

17 

17 

13 

-     : 

- 

- 

4 

21 

17 

17 

,   17 

13 

- 

- 

} 

5 

25 

21 

I   17 

:  17 

17 

13 

- 

\   ~ 

1 

}   6 

!,-.  25 

21 

21 

17 

17 

17 

13 

\ 

7 

29 

25 

21 

21 

17 

17 

17 

13   ! 

ECCENTRIC  FOUNDATION  LOADS 

The  shifting  position  of  live  loads,  even  in  a  building,  commonly 
makes  it  impossible  to  compute  exactly  the  point  of  application  of  the  resultant 
foundation  thrust  for  combined  dead  and  live  loads,  especially  for  bearing  walls 
or  wall  columns.  ^  common  case  is  that  shov/n  in  Fig.  12,  where  the  resultant 


'•'     .  •    ' 


59 

pressure  P,  including  the  live  load,  is  considerably  removed  from  the  line  of 
action  Q  for  the  dead  load  only. 

Frequently  it  is  specified  that  the  resultant  from  any  possible 
combination  of  dead  and  live  Icx'ds  must  fall  v/ithin  the  middle  third  of  the 
foundation  bed.  Therer.son  for  this  spocificrtion  is  nr.de  clearer  by  the  follow- 
ing analysis.  Many  times,  it  is  impossible  or  impracticable  to  get  the  centroid> 
of  the  foundation  area  opposite  the  center  of  lording  on  account  of  the  varying 
live  lords.  In  such  cases  tho  pressure  intensity  is  not  uniform  over  the 
foundation  area,  but  varies  linearly  from  a  maximum  at  that  edge  of  the  footing 
which  is  nearer  to  the  center  of  pressure,  to  a  minimum  at  the  other  toe.  In 
Fig.  13,  with  a  full  live  load  acting,  lot  the  resultant  of  the  beam  reaction 
PI,  and  the  wall  load  PW  equal  P.,  acting  at  the  point  b,  whose  distance  from 
either  of  the  loads  can  b  e  found  by  the  principle  of  the  lever.  Suppose  b  to 
be  within  the  middle  third  of  the  base.  Let  A  be  the  area  of  tho  rectangular 
foundation  bed,  whose  width  is  d  and  length  1.  The  stress  diagram  for  the 
foundation  pressure  intensities  is  trapezoidal.  A  semigraphical  solution  for  the 
maximum  and  minimum  foundation  pressures  s^  and  sg  in  terms  of  the  average 
pressure  and  the  eccentricity  p,  of  the  applied  load,  gives:-  taking  static 
moments  for  the  stress  diagram  ares-.s  about  b, 


p  (ds?)  =(d/6  -  p  )(  d(ai-B2)     .........  .......  (1) 

2 
Solving  for  p, 

p  =  d/6(si-sp)   ........................   (2) 

Hi-  —  —  i 

l*l+»2' 
But  Pr  =  A  (BI  +  s2)     .  ........................   (3) 


2 

Equating  (2)  and  (3)  asjsiraultaneous  equations: 

S-L  =  Pr  /A  (1  +  6p/d)   ....................   (4) 

s2  =  Pr/A  (1  -  6p/d)  .....  .................   (5) 

Equations  (4)  and  (5)  maybe  derived  from  Fig.  13  more  simply  by 
talcing  moments  about  the  third  point  of  the  joint  which  is  nearer  si.  The 
static  moment  of  the  rectangle  s2d  about  a  point  d/3  from  si  is  precisely  the 


'     ' 


•' 


60 
same  as  the  static  moment  of  the  trapezoidal  about  the  same  point,  because 

the  moment  of  the  triangle  (BI  -  sg)d  about  that  point  is  zero«  Hence,  since 

~~Z~ 

the  moment  of  Pr  and  that  of  the  upward  pressures  must  balance  about  any  point, 

Pr  (d/6  -  p)  =  s2Ad/6. 

Solving  for  S£  we  g et  equation  (5);  substituting  that  value  of  3%  in  equation 
(3)  and  solving  for  s^  gives  equation  (4).  Consult  V/egman,  Design  and  Con- 
struction of  Dams,  Chap.  2,  pp.  8-13;  Morrison  and  Brodie,  High  Masonry  Dam 
Design,  pp.  7  -  14. 

If  the  total  loed  P   were  axial,  so  that  p  =  0,  the  pressure  in- 
tensity on  the  bed  would  be  constant  and  s  =  Pr/A •  .•  •  (6) 

In  this  case  the  pressure  diagram  becomes  a  rectangle  of  breadth  d  and  height  s. 

xhe  increase  and  decrease  of  pressure  intensity  due  to  an  eccen- 
tricity p  is  ±  6pPr/dA.   For  usual  calculations  a  unit  length  of  wall  is 
considered.  Making  1  ~  1,  A  =  d,  equations  (4).,  (5)  and  (6)  become: 

S;L  =  Pr/d  (1  +  6p/d)  .....;.,.........    •  •  •  •  (41) 

s2  =  Pr/d  (1  -  6p/d) .  .  .  (01) 

s  =  Pr/d .  .  (6') 

In  equation  (41),  (5')  and  (6')  Pr  becomes  the  lord  per  lineal  foot  of  wall. 

When  p  =  0,  s  =  Si  =  S2  =  Pr/d  ........  .........   (7) ) 

V/hen  p>  0  bpt  ^  d/6,    equations    (4),    (5),    (4')  and   (5')   stand. 

When  p  =  d/6,   s-L  =  2Pr/d;   s2  -  0 .-    •'   • (8) 

When  p^  d/6  bpt^d/2,  consult  a  later  paragraph  and  fig.  17 

Notice  in  the  above  demonstration.,  if  p  =  d/6,  so  that  the  load  Pr 
is  at  the  middle  third,  thct  BI  is  twice  the  average  pressure  end  s2  is  zero. 
The  pressure  diagram  becomes  a  triangle;  see  Fig.  14.  If  p  is  greater  than  d/6, 
S2  changes  sign  or  becomes  a  tensile  stress,  which  ordinarily  cannot  exist  at 
the  junction 'of  masonry  and  the  foundation  soil,  and  should  not  exist  at  higher 
levels  in  the  masonry  itself;  see  Fig.  15.  A  possible  exception  is  found  in  the 
case  of  a  pile  grillage  fbunC.E.tion  with  the  tops  of  the  piles  imbedded  in  con- 
crete. Here  a  small  t ensile  stress  occas  ionally  -might  be  allowed.  If  p  ^  d/6 


•'     f"  t  " 

-  •  • 

3  3ffio  06  d  'irrASSi  i> "  &'  -  ? .  n I 


'  $    ~ 


a-ixa.  ?' 


61 

Fig.    13,   the  resultant  pressure   lies  within  the  middle   third  of  the   foundation 
base,   the  stress  diagram  is    trapezoidal,    and  the  analysis   shows   that  no  tensile 
stresses  can  exist.    It   is  usually  specified  that  the    footing  must  be  spread, 
making  d  sufficiently  large,   so  that,   under  all  possible  conditions,   the 
resultant  pressure  will  pass  through  or  within  the  middle  third  of  the  area  of 
the  foundation  base,    thus  avoiding  a  possible  tension  for   S2« 

An  analysis   for   foundation  pressures  differing   from  the  preceding 
treatment,  but  leading  to   the  seme   conclusions  can  be  made  by  assuming  the 
foundation  pressure,   Fig.    16,    caused  by  a  load  Pr  acting  at  the   center  of  the 
footing  C,  resisted  by  the  rectangular  portion,  ajcf,   of  tha  pressure  diagram 
considered  as  concentrated   in  R  =  1/2   (s^  +  SojcLl;   and  by  a  couple  Pr  x  p, 
resisted  by  the    triangular  portion,   hfghie,    of  the  diagram.    The   foundation  bed 

* 

then  may  be  analyzed  for   stresses  as  a  beam  of  rectangular  section  subjected  to 
direcfi  compression  PL  and  to   cross  bending  stresses;  max.    fiber   stress  k  =  ei   = 
fg  =   (s     -  sg)       caused  by  the  bending  moment  M  =  Prp.        Let  k  =   (s^  -  s^}   a. 

' 


•  . 

the  maximum  unit    fiber  stress  due  to  the   bending  moment;   I  =  Id3/12  =  the 
moment  of  inertia  of  c  roe  s  section  of  dimensions  1  x  d;   then,  from  the  general 
formulae  for  flexure   in  b  earns  ,   neutral  axis  at  C,    the  external  bending  moment 


is : 


M  -  Prp  =  +(si  -  s?.)l  =  (si  -  sp.  )  Id2     .  .  .  .  .......   (9) 

d  12 


k  =  si  -82     ~     ±  6Prp/ld2  =  6Prp/Ad    ' 


The  resultant  stresses  Sj  and  s2  equal  the  average  stress  Pr/A 
caused  by  the  central  load  Pr,  respectively  plus  and  minus,  the  bending  stress 
k,  giving  values  for  sx  and  s2  identical  with  those  in  equations  (4)  and  (5) 

TREATMENT  FOR  CEHTSR  OF  PRESSURE  WITHOUT  THE  MIDDLE  THIRD 

Fig.  17  ;  see  also  Fig.  15.  When  the  ecceiitricity  p  is  greater 
than  d/6,  the  center  of  loading  b  for  the  resultant  Pr  falls  outside  the  third 
point  t.  Ordinarily  it  is  assumed  that  th.e  joint  Id  C£.n  tcJce  no  tensile  s  tresses, 


62 

It  is  assumed  that  tho  Jiodror 'oaooarjr  JeinJ  cracks  from  f  to  h,    fig.   17.   The 
tensile  stress  diagram  hfg  is  neglected.   By  analogy  to  the  case,  when  p  =  d/6, 
see  fig.   14,   the  effective  joint   length     ho_  is  taken  equal  to  3  u.   The  unit 
stresses,  diagram  hei,    for  the  foundation  bed  he,  area  =  3  u  x  1,  will  vary 
uniformly  from  a  maximum  value  sj.      to  zero  at  h.   The  average  stress   is  sj/2,    end 

acts  upon  the  area  3  ul.     Pr  =     3  s-jul       ,   hence  S}  *  2  Pr     . 

2  3  ul 

In  general,   to  design  a  foundation  bed  without  tension,   if  u  is   the 

minimum  allowable  distance  from  the  outer  toe  e  to   the  point   of  application  b  of 
the   resultant   load  Pr,    fig.    17,   then  3u  is  the  maximum  effective  width  of  the 
foundation.-    If  ss-^  is  the  maximum  allowable  unit   foundation  pressure,  Pr  the 

maximum  load,   then  Pr  -  5  si   ul       and  3  u  =  2  Pr  .      It  should  be  noted  that  the 

2  sxl 

expression  1,1  -  Prp  =  ±  kl_     is  perfectly  general,  v'o  may  consider  1.1  to  be  the 

r 
external  bending  moment  caused  by  any  number  of  horizontal   or  inclined  forces 

acting  above  the  given  bed  or  joint.    I   is  the  moment   of  inertia  of  the  cross 
section  of  the   foundation  bod  or  masonry  jjoint,     which  maybe  square,  circular, 
rectangular  or  annular,  as   in  the  case  of  chimneys.   Here  r   in  all  cases   is   the 
distance  from  the  ccntroid  of  the  cross   section  to  the  extreme  point   or  too,   at 
which  the  raximum  intensity  of  pressure  s-^  exists.   S..c  Turneaure  &  I.Iauror,   ed. 
1919,   p.   435,   Fig.    12, 

PBESSURE  ON  THE   FOUNDATION    BED  OF  A  ii'.SQMBY  PI£R 

A  general  problem  will  now  be  outlined   for t he  design  .f  the   foun- 
dation for  a  masonry  bridge  pier.   Structures  of  this  typo  arc   subject   to  a 
variety  of  horizontal   forces,    such  as  wind,    ice  pressure,   dynrmic  pressure  frcm 
flowing  water,   tractive  forces    from  moving  "trai  ns ,  r.nd  possible  blows    frtnm  ships 
or  drift  wood,   a  detailed  consideration  of  which  more  properly  belongs   to  the 
treatment  of  the  design  of  mrsonry  structures.   V/ind  pressure    only  will  be  assumed 
here.    If  other  horizontal  forces  were  acting,    it  vould  bo  necessary  to  compute 
for  their  the   total  sum  of  the  moments  at  the   foundation  bod.    For   simplicity  a 


-v    ;.  •/••i-rii'.i-j   '; 


........ 


••:          ..'          - 


'-Tf      j 


63 

Consult  Brkor,  A  Treatise  on  nasonry  Construction,  Chap.  20, 
Bridge  Piers,  ed.  1909,  pp,  551-563;  r.lso  the  Irter  reticle  in  these  notes 
entitled  Design  of  a  Railway  Bridge  Pier,  particularly  paragraphs  15-37  inclusive. 

In  Fig.   18  let  H.=  the  resultant   of  the  horizontrl    wind  pressures 
on  pier  and  trus.es   considered  as  applied  at  a  distance  a  above  the  pier   footing. 
Let  d  =  the   length  of  pier    footing.   Let  P  =  the  resultant  w  eight   of  the  bridge, 
bridge  pier,    and  footing,   applied  at  the  center  C  of  the    footing  bed.    The 

length  d  must  be  so  adjusted  by  design  calculations  that   the  ;naxiraum  pressure 

due  to  P  and  to  the  moment  of  the  wind  pressure  H, 

will  not  exceed  the  allowable  b  earing  power  on  the   soil.    The  problem  is   incapable 

of  a  direct  solutionbecau.se  the  weight  P  is  not  known  definitely  until   the 
length   d  is  determined.    Let   S]_  =  the  max.   allowable  bar.  ring  power  of  the   soil, 
a     value  to  be  reached  at  the   leeward  toe  A.    It   is  composed  of  two  components, 

s  and  k.        s  =  si   +  53          is  caused  by  the   direct  lord  P,  k  by  the  bending 

~~2~ 
moment'  Ka  from  the  v/ind  -ores  sure.    The  bending  moment  Ka  =  gkl   .    If  1  =  the  vddth 

d 
of  the  pier  footing,   normal  to  the  plane  of  the   figure,   the  moment   of  inertia 

for  neutral  axis  at  C   is  Id3/12  .      The  area  of  the    foundation  bed  is   Id.   Hence: 

sl  =  s   +  k  =  P/ld  +  Had/21 
Similarly  s2  =  s  -  k  ....... 

Suppose  D  is  the  point   of  intersection  of  the  forces  K  and  P.   By 
constructing  the  rectrngle   of   forces,    the  diagonal  R  represents  completely 
resultant  thrust  upon  the  bed  dl.    It  cuts  the  bed   in  the   center  of  pressure  D,   . 
wjiich  for  the  stress  diagram  as  dravm  lies  within  the  third  point   B.  rvith  the 
point  fl  determined  the  distance  CO  is  the   eccentricity  p.    For-milr.s    (4)  rnd   (5) 
give  the  values   of  sI  and  s2-   These  values  must  check  the   results   obtrined  by 
equati  ons    (  11  )  and   (  12  )  „ 

2 


If  s   =  k,   s     =  0,   the  stress   dirgram  becomes  a  triangle;    ai 


,  ,  (13) 

2P/ld  =  Had/I     .,.......••••    

When  tension  in  the  bed  is  prohibited  by  specification,   eouation  (13) 


determines  the  mininum  allowable  v:- lue  for  d.    Solving  for  d   fro*  the^laet 
members  of   ecuation  (IS),   d  =  6  Ha/P.    ...«*•  


64 

Equation  (14)  shows  that  d  is  independent  of  1,  rs  it  should  be. 
For  soft  soils  it,  usually  implies  too  Ir.rge  a  value  £or  s^.  In  such  cases,  for 
safety  from  possible  settlement,  the  point  D  must  lie  within  the  middle  point  B. 
Equation  (11)  then  give's  the  value  of  d  in  terms  of  Sj.  Substituting  for  I  in 
equation  (11)  :- 

*  i 

sl  =  P/ld  +  6Ha/ld2  =  Po/d  +  6  H0a/d20   Here  P0  and  HQ  are  values  for 
1  =  unity.  Solfing  for  d:   d  =  P0/2si  ±  A  /6H0a  ~P^~    .........  (15) 


81 

Notice  that  equations   (11),    (13),    (14)  and   (15)   are  perfectly 

general.    They  cou,M  be  used  to  determine  the  max.    stress   or  joint   length  in  any 
horizontal  section  of  the  masonry.    They  also  are  applicable  where  a  moment  M  is 
caused  in  any  manner,  as  by  earth  or  water  pressure.   In  each  case  the  moment   is 
to  be  calculated  for  a  moment  center  in  the   level  of  the  section  c  ons  id  or  ed. 

STABILITY  AGAINST  SLIDING 

In  Fig.    18  9  is  the  angle  which  R  makes  with  the   vertical.    The 

verticrl   component   of  E  is  P.    If  f  is  the  coefficient  of  friction  for  the   footing 
upon  the   foundation  b  ed,    then  by  the  law  of  friction  F  =  Pf.     F  is  the   total 
frictional  force  exerted   in  tho  bod.    Let  q  =  the   intensity  of  shearing  tenacity 
between  the   footing  rnd    ;-bed.   Tho  total   shearing  strength  offered  is  Q  =  qld. 
For  equilibrium  against  sliding:- 

H-  F  +  Q  =  Pf  +  qld   .....    .....    .    ......    .    .    (16) 

Commonly  in  equation  (16)  the  term  .for  shearing  tenacity  is  neglected  or  consider- 
ed a  reserve  factor  for  safety.  Then 


H^F  =  Pf 


f  ±     H/P     =  tan  9   .....    ,    .............. 

Knee   for  safety  tan  9  must  be   less   than  the  coefficient   of  friction.    Generally 
f  is  equal  to  or  less  than  0.67  for  masonry.    For  deep  foundations  the   effective 
load  producing  friction  on  the  bed  should  betaken  less  than  P.    Buoyancy  from 
water  or  silt  and  skin  friction  on  the  sides  of  the    foundation  vl.3n  founded  in 

sr.nd,    clay  or  other  granulrr  masses  will  reduce  the   value   of  P  very  decidedly. 
On  the   other  fend,    foundations   floating  in  granular  deposits  will   be  retained 


I 

against  lateral  movement  by  the    thrust  action  or  abutting  power  of  the  surround- 
ing material.   For  a  bridge  pier,    like  that  shown  in  Fig.    18,    the  load  P  cor/nonly 
is   so  large  compared  with  H  that  the  safety  against  sliding  is  jreat.  Usually  no 
investigation  for  sliding  stability  isxecpired.  An  inquiry  for  sliding  should 
be  made  when  H  is   large  and  P  small,  particularly  if  the   footing  is  deeply  sub- 
merged in  water  with  no   solid  material   surrounding  the   structure  above  the  level 
of  the  bed. 

Numerical  Example;     Design  of  a  Pier,   Fig.    18.     Weight   of  super- 
structure 327.5  tons.    Let  the  wind  pressure  =  30  Ib.  per   sq.    ft.     Assume  the  max. 
allowable  pressure  s^   =  3  tons  per  so.    ft.      Let  h  =  40  ft. ;   top  dimensions   of 
pier  3  x  20   ft.;   dimensions  at  top  of  footing  =  7  x  26  ft.    The  pier   is  to   be 
built   of  concrete  weighing  150   Ib.  per  cu.    ft.    The  approximate  weight  of  pier 
above  the    footing  is    (3  x  20)    +   (7  x  26)        x  40  x  150   =  726,000  Ib.    =  363  tons. 
The  unit  pressure  at  the  top^of  thd   footing,   for  vertical  loads   only  is 
327, 5  +  363  =3.8  tons  per  sq.    ft.        Suppose  the  wind  on  the  superstructure  = 

7  x  26 

300  Ib.   per  lineal  ft.    for   two  100    ft.  spans;  then  H  =  300  x  100  =  30,000  Ib.    = 
15  tons.      Let  H  act  15  ft.   above  the  pier  top.    For  simplicity  assume  the  entire 
pier  exposed,    that   is,    let  the  ground   level  be  at  the  top  of  the  footing.   The 
wind  pressure  on  the  pier  =  1/2   (   3+7)  x  40  x  30  =  6000   Ib.    =  3  tons.    It  acts 
approximately  20  ft.  above   the  top  of  the   footing.   The   lever  arm  of  the  wind 
pressure  on  the  pier   is  really  the  distance  from  the    footing  top  to  the  centroid 
of  the  trapezoidal  end  face  of  the  pier,  somewhat   less   than  20  ft.     The  total 
wind  moment  about  the  footing  -coo  is  15  x  55  +  3  x  20  =  885  ft.   tons.    By 
formula   (11)   sx  -  3.8   +  (885  x  IS)   -t-  7  x(26)3  -     3.8   +  1.1  =  4.9  tons  per  sq.ft. 

12 

*  68.  Ib.  per  sq.    in.      Concrete  ma;  safely  take  400   Ib.  per  sq.    in.    in  compression. 
The  pier  base   therefore   is   excessively  strong.   This  is  usually  the   cr.se  since  a 
pier  must  have  sufficient  plan  to  support  the  superstructure. 

The   footing  of  concrete  is  assumed  5  ft.    in  depth,    12    ft.  wide  anc 
30   ft.    long.   Its  weight    is   12    x  30  x  5  x  150  =  270,000   Ibs.    =  135  tons.   The  total 
vertical  load  on  the  foundrtion  bed  =  327.5  +  363   +  135  =  825  tons,   giving  an 
average  pressure  s  =  825  =  2.3  tons  per  sq.    ft.      For  t  he   founda.tion  bed:- 

12  x  30 
M  =  15  x  60   +  3  x  25  =  975 'tons;      I  =  12  x   (30)*     =  27,000  ft.4;  hence 

12 
sl  =•  2.3   +  975  x  15  =  2.3   +  0.5  =  2.8  tons  per  sq.    ft.,  which  is    sufficiently 

27000 

close  to   the  r.ssuned  allowrble  pressure  of  3  tons  to  make   further  calculations 
unwarranted.   Note  that  k  =  0.5  tons  por  sq.   ft.  „  e2  «  r.  -  k  =    2.3  -  0.5  =    1.8 
per  SQ.    ft.      It  is    to  be  observed  that   for  neither  joint  does  tension  occu 
the  windward  toe.   The  center  of  pressure   is  well  within  the  middle  third 
level;   its  position  may  be  located  easily  by  graphics,   or  calculatec 
moments  about  the  point  D. 

Study  in  Taylor  and  Thompson,  Concrete,  Plain  and  Reinforced,  ed. 
1909,   the    design  for  an  arch  abutment,  pp.    583-586.    On  page  586_is  described  a 
graphic   method   for  determining  the  maximum  and  minimum  inteiisi 
pressure  for  eccentric  loadings. 


,-    Si,/5)        '.V 


66 

In  Fig.  18a  let  AB  be  to  scale  the  length  d  of  the  foundation  bod 
of  Fig.  18;  let  C  and  D  be  the  thirdpoints  of  the  joint.  0  is  the  center  of 
pressure  for  the  resultant  thrust  R  whose  horizontal  and  vertical  components  are 
respectively  K  and  P.  Find  the  average  unit  pressure  s  by  dividing  the  totc.1 
thrust  R  by  the  area  d'l,  which  area  is  the  projection  of  the  bed  dl,  drawn 
perpendicular  to  the  thrust  R.  The  point  E  is  the  center  of  the  joint  d.   Plot 
the  average  unit  pressure  s  as  FG  to  any  convenient  scale,  perpendicular  to  the 
projection  to  the  base  at  its  center  F.  Connect  the  projected  third  points  J 
and  K  with  G  and  prolong  J(J  to  M  on  the  prolongation  of  tlie  thrust  R.  The  line 
GK  cuts  R  at  N.  QN  =  S£  and  QM  =  si.   The  shaded  trapezoid  is  the  unit  pressure 
diagram  . 

SPREAD  FOOTINGS 

Where  building  columns  or  walls  are  founded  upon  sand,  earth  or 
other  loose  materials,  at  shallow  depths,  it  is  often  necessary  to  design  foot- 
ings to  distribute  the  total  foundation  load  over  an  extended  plan  in  order  to 
reduce  the  intensity  of  pressure  to  low  values.  This  result  may  be  effected  in  a 

variety  of  ways,  by: 

1.  timber  footings; 

2.  offsets  of  masonry  in  rubble,  brick  or  concrete 

3.  timber  jprillages   or  rafts 

4.  im^rted  arches  of  stone,    brick,   concrete  or  reinforced 

concrete 

B.  footings\of  structural  steel  bea.ns  and  concrete 
6.  footings  of  reinforced  concrete. 


1.   TIMBER  FOOTINGS 

Fig.  19  illustrates  a  simple  timber  footing  designed  to  support  a 
column  load  ard  distribute  it  over  a  foundation  bed.  Such  footings  give  excellent 
service  for  very  soft  material,  but  as  permanent  structures  they  should  not  be 
used  unless  the  timber  is  always  wet.  The  footing  is  composed  of  platforms  of 
sticks  in  layers  laid  at  right  angles.  The  amount  that  a  course  of  timbers  may 
project  beyond  the  one  next  above  it  is  found  by  treating  the  projection  as  a 
cantilever  bean  supportad  from  above  and  loaded  uniformly  from  be  low.  (Consult 
tlie  next  article,  equation  (19)  and  Fig.  20  with  accompanying  examples).  The 
maximum  allowable  fiber  stress  in  the  timber  generally  is  taken  at  1000  Ib.  per 
sq.  in.,  When  possible, and  costs  do  not  prohibit,  the  footing  is  made  more  solid 
and  permanent  by  supporting  the  lowest  layer  of  timbers  upon  a  bed  of  concrete 

6  to  12  inches  in  thickness.  See  Kidder,  Architects  ai}.d  Builders  Pocket  Book, 
ed.  1908,  pp.  170-171;  Froitag,  Architectural  Engineering,  «l.  1911,  Chsp.  9, 


-. 


:;  : 


•"•* 


,« 


i  .-> 


67 

pp.  312  -  314;  Jacoby  and  Davis,  Foundations  of  Bridges  and  Buildings,  Chap.  15, 
Art.  156;  Williams,  Design  of  Masonry  Structures  and  Foundations,  p.  445. 

2.  I.1ASMBY  OFFSETS;  RUBBLE.  BRICK  OE  CONCRETE 
The  amount  of  projection  m,  Fig.  20,  for  masonry,  concrete  or 
brick  offsets  is  calculated  in  the  same  manner  as  for  timber,  by  assuming  the 
offset  to  be  a  uniformly  loaded  cantilever,  fixed  at  the  edge  AA  of  the  overlying 
layer  or  tier.  Let  R  in  Ib.  per  sq.  in.  =  the  modulus  of  rupture  of  the  material; 
let  t  in  inches  be  the  depth  of  footing  course.  The  load  intensity  per  unit  of 
breadth  upon  the  foundation  bed  is  s  in  Ibs.  per  qq.  in.  feting  from  below, 
uniformly  distributed.  The  max.  bending  moment  at  A  is  1.1  =  sm2/2,  which  accord- 
ing to  the  common  theory  of  flexure  is  equal  to  2  Rl/t.   I  =  t^/12,  is  the 
moment  of  inertia  of  the c ross  section  of  the  projecting  offset,  for  rectangular 
cross  sections.  Hence  sm  /  2  =  Rt2/6;  and  m,  the  allowable  projection,  is 
t  YR/SS.    If  p  is  the  pressure  in  tons  per  sq.  ft.  on  the  base, 


m  =   tf_R =  0.155 

J5(20QO)P 

r     444 

It  is  sufficiently  close  to   assume  that  m  =  t/6/\/R/P (20) 

If  R  in  formula   (20)   is   the  modulus  of  rupture   it  gives  a  value  for 
m  for  which  thq  offset  is  just  at  the  point  of  failure  at  A.     A  large  safety 
factor  usually  is   imposed  for  masonry  or  brick  or  timber  construction,   so  tha.t   in 

using  the  formula,  R  should  be  taken  as  the   safe  cross  breaking  strength,   supply- 

A  factor  of  safety  of  15  to  20  is  not  uncommon  for  masonry.  -^ 
ing  a   safety  factor  of  5  to  20,   according   to  the  grac".e   of  rnaterial.^The  above 

analysis  and  the    following   table  are   taken  from  Baker's  Treatise   on  Masonry  Con- 
struction,  10th  ed.,   pp.   356-357.    The  table  gives  approximate  safe  values   foi   R. 


68 


Safe  Off -Set  -£pr  Masonry  Footing;  Courses,   Using  10  as  a 


Factor  of  Safety.    ( 

For  limitations,    see  Arts.    698-701,   Baker.) 

IKind  of  Stone 

R,    in                   Offset 

in  terms 

of  the 

- 

•Ib                          thickness  of  the 

course 

I 

per                       for  a 

pressure  in  tons 

j 

sq.                        per  sq 

.ft.   on  the   bottom 

in. 

of  the 

course  of 

j 

0.5 

i.o  | 

2.0     j 

Stone,   Bluestone,  North  River 

5026 

4.5 

3.2    | 

2.3 

Grani  te 

1849 

2.7 

1.9 

1.4 

Limestone 

1377 

2.4 

1.7 

1.2 

Sandstone 

1 

1378 

2.4 

1.7    ; 

1.2 

Brickwork:  good  building  brick 

in  poor 

j 

i 

1:2  natural  cement  mortar, 

age  50 

| 

! 

days. 

120 

0.7 

0.5    i 

0.3 

Under-burned  building  bi 

ick  in 

j 

1:3  Portland  cement  mortar, 

ag^e  76 

days 

706 

1.7     ' 
*•  '      i 

1.2  i 

0.8 

Vitrified  building  brick  in  1:3 

i 

Portland  cement  mortar,  age   76 

days 

3560                          4.3  : 

2.7  ' 

1.9 

Concrete,   1:2:4  Portland  cement 

at  one  mo. 

300                        1.1 

0.8  ' 

0.5 

it                  ti 

11      6  mos.      400                       1.4 

0.9 

0.6 

For  granite  maso  nry,  v/here  the  modulus  of  rupture  R  is  taken  at 

1800  Ib.   per  sq.    in.    if  a  safety  factor   of  6  is  used  and  the  allowable   load  on  the 
foundation  bed  is  2   tons  per  sc.    ft.,    the    formula  gives  m  =  t/6/J 300/2  = 
approximately  2.04  t.      In  applying  the   formula  to  masonry  construction,   the   pro- 
jecting stones  must  be   imbedded  beneath  the  upper  course   far  enough  to   firmly  fix 
them,  a  distance  equal  tort  least   one-half  their  length.   In  the  example  the 

granite  blocks  should  have  a  length     =     4.08  t.    The  safe  strength  of  the  mason- 
ry in  direct  compression,  which  depends   largely  on  the  Strength  of  the  mortar 
used,   must  not  for  any  course  be  exceeded.  Notice   in  the  design  of  piers,   built 
Yvlth  a  number  of  offsets,   that  as   the  section  area  of  the  pier  d  ecreases  tov/ard 
the    top  courses,  the  unit  load  increases,   hence,   the  possible  length  of   offset 
decreases    from  the   bottom  upward;   Fig.    20,  m^  m-j_>  mg. 

For  timber  offsets,   if  the  safe  value   of  R  is  taken  at  1000  Ib.  per 
sq.    in.   and  ?  =  1   ton  per   sq.    ft.,    then  m  =  t/e^jToOO  =  5.3  t;    if  P  =  2  tons  per 
sq.    ft. ,  m  =  3.7  t, 

This  method  for  determining  offsets   is  as  equally  applicable   to  a 
layer  of  a  timber  gri  Huge  if  t/.e  timbers  are   laid  close,  as  to  a  course  of  a 


'•>'     ••-••     , 


"•> '  '>  ••       '  '• 


69 

masonry  stepped  pier.   If  timber  grillages  are  designed  so  that,  wide  spaces  are 

left  between  the   timbers.    Fig.    19,    the  bending  moment,  M,   should  be  calculated 
by  considering  the  actual  concentrated  loads    fnum  the  underlying  beams. 

Figures  21,  22  and  23  give   examples   of  simple  masonry  offsets  for 
light  buildings  of  types   common  20  to  30  years  .a  go.    In  more  elaborate  and  heavier 
designs  the    footings  and  walls  might  have  a  greater  number  of  steps.    Footings 
of  this   type  are  now  generally  constructed  of  concrete,    but  they  may  be  made   of 
dimension  stone.    In  either  case  the  amount   of  projection  for  any  course  can  be 

determined  by  the   theoretic  principles   of  the  preceding  paragraph,   though  such  a 

,  * 

refinement  is  hardly  necessary.  For  upper  walls  general  rules  prescribe  the 

successive  thickness.  If  the  depth  of  any  footing  course  be  made  at  least  twice 
its  max.  projection,  good  practice  usually  will  be  satisfied.  For  dimension 
stones  the  depths  of  courses  vary  from  18  inches  to  3  ft.jfor  concrete  they  may 
be  taken  12  to  18  inches. 

The  Boston  Building  Law  (of  about  1890)  requires  that  the  foundation 
block,  Fig.  21,  of  a  pier  or  column  shall  be  at  least  24  inches  greater  in  plan 
than  the  pier  or  pedestal  that  rests  upon  it.  Thus,  the  distance  AB,  Fig.  21,  must 
be  12  inches  or  more.  For  rubble  foundation  walls,  Fig.  22.  gives  requirements 
of  the  Boston  Law.  That  law  does  not  allow  rubble  foundation  under  walls  of 
buildings  over  40  ft.  high,  with  the  exception  of  "third  class  buildings  outside 
the  limits".  The  bed  of  foundation  must  not  be  less  than  4  ft.  below  the  frost 
line.  Two-thirds  of  the  bulk  of  the  wall  must  consist  of  through  stones, 
thoroughly  bonded.  The  concrete  base  must  be  at  least  12  inches  wider  than  the 

» 

fir^t  rubble   course   above  it.    For  granite  block  work-,   Fig.   23,   there  c.re   similar 
requirements.   In  both  cases  the  concrete  footing  shall  not  be  less  than  12  in, 
thick;    if  of  stone,   not   less  than  16   inches. 

The  f o 11 owing  table  shows  the  thickness- of  brick  and  rubble  found- 
tion  walls  and  concrete  footings,  Fig.  22,  as  prescribed  by  the  Boston  regula- 
ions  just  cited.  For  every  10  ft.  height  of  portion  b,  or  fraction  thereof,  an 


f   •!.•:•• 


••':'. 


•       > 


70 


additional  thickness  of  5  inches  mu5 1  be  added.  At  least  the  same  amount  of 
thickening  is  also  demanded  for  the  footing  C. 


Thickness   of  brick 
wall,    inches 

a          j 
inches  ! 

b                        c 

inches       i-        inches 

8 
12 
16 
20 

20 
25 

30      \j 
35        ! 

25                         37 
30                         42 
35                         47 
40                         52 

The  following  table  shows  corresponding  values  for  granite  block 
foundations,  Fig.  23: 


Thickness  of  brick 
wall  ,  inches 

a 

inches 

b 

inches 

c 

inche  s 

8 
12 
16 
20 

16 
20 
-  24 
28 

20 
24 
28 
32 

32 
36 

40 
44 

The  following  extracts  are  from  the  1901  New  York  Building  Code, 

Section  26:-  "Foundation  walls  shall  be  built  of  stone,  brick,  Portland  cement 
concrete,  iron  or  steel.  If  built  of  rubble  stone,  or  Portland  cement  concrete, 
they  shall  be  at  least  8  inches  thicker  than  the  Trail  next  above  them  to  a  depth 
of  12  ft.  below  the  curb  level.  For  every  additional  10  ft.,  or  part  thereof, 
deeper  they  shall  be  increased  4  inches  in  thickness.  If  built  of  brick,  -they  shall 
be  at  least  4  inches  thicker  than  the  wall  next  above  them  to  a  depth  of  12  ft. 
below  the  curb  level;  and  for  every  additional  10  ft.  or  part  thereof,  deeper, 
they  shall  be  increased  4  inches  in  thickness".   The  concrete  footings  are 

required  to  be  at  least  12  inches  thick.  If  footings  are  built  of  stone,  the 
stones  must  be  not  less  than  2  ft.  x  3  ft.  and  at  least  8  inches  in  thickness 
for  walls;  and  not  less  tjhan  10  inches  in  thickness  if  under  piers,  columns  or 
posts.  Footings  of  concrete  or  stone  are  required  to  be  at  least  12  inches  wider 
than  the  bottom  width  of  walls.  If  stepped-up  footings  of  brick  are  used  in 
place  of  stone,  above  the  concrete,  the  offsets  if  laid  in  single  courses,  shall 
each  not  exceed  1  1/2  inches,  or  if  laid  in  double  courses,  then  each  shall n ot 
exceed  3  inches,  offsetting  the  first  course  of  brick  work  back  one-half  the 

t 

thickness  of  the  concrete  base,  so  as  to  properly  distribute  the  load  to  be 
imposed  thereon.  Similar  requirements  for  footings  are  found  in  other  building 
codes.  It  is  recommended  that  students  consult  foundation  clauses  in  the  building 

ordinances  of  the  cities  -of  New  York,  Boston,  Philadelphia,  Chicago,  St.  Louis, 

\ 
and  San  Francisco.  , 


tf. 


71 . 
< 

As  concluding  examples,   Figs.   23A  and  23B  v;ith  discussion  are 

extracted,  from  the  International  Correspondence  School  pamphlet,  Structural 
Engineering  Course,   Statics   of  Ilcsonry,   Pert  2,  pp.    12-17. 

The  dosign  for  a  heavy   foundation  pier  supporting  an  interior 

column  for  a  Class  C  building  is  shown  in  Fig.  23A.   "The  footing,    if  of  concrete., 
should  never  be  less   than  12   inches  and  is  sometimes  rrp.de  16  or  18   inches   in 
thickness.    The  projection  of  the    footing  beyond  the   brick  work  should  not  be 
greater  than  one-half  the  thickness   of  tho   footing  and  nover  more  than  8  inches. 

The  batter  of  the    bripk  work  at  the   sides  should  not   be  greater  than  6  inches  in 

. 
every  foot  of  rise.   The   thickness  t   of  the  capstone  should  equal  1/4  the  length 

of  its  side,    or  W/4,   though  when  the  capstone   is  rectangular,  t  he   thickness  may 
equal  1/5  of  the  longer  dimension.    In  no  case  however  should  the  capstone  be 
less  than  10   inches  thick." 

In  Fig.  23B  Iff t  the   load  on  the  cast  iron  base  supporting  a  wood 
column  be  200,000  Ibs.   Design  for  this  column  a  foundation  pier  made  of  brick 

work  in  cement  mortar  *.ath  concrete  br.se  and  granite  cap.   Tha  soil  under  the 

\ 
pier,   being  compact  gravel  and  send,    can  safely  sustain  6  tons  per  sc.    ft.  But 

assuming  a  inaxiiaum,  load  of  only  3  tons  the   base  area  is  33.5  sc.    ft.    or  5'9"  sq. 
If  the  bearing  value  of  brick  work  in  Portlsnd  cement  mortc.r   is  200  Ib.  per  sq. 

in.,    the  granite  cap  must   supply  a  plan  area  of  1000  sq.    in.   =  6.94   sq.    ft.,   or 
j  » 

2*8"   square.   For  further  discussion  c onsult  the   original  reference. 

3«    TIMBER  GRILIA&ES   PR  HAFTS 

Fig.  24  exhibits  a  timber  grillage  cons  is  tins  a?  three   layers   of 
timbej;   (spaces  filled  with   concrete)   resting  upon  piles.    The  grillage  platform 
supports  itone   or  brick  masonry.    Such  a  grillage  may  be  built   of  timbers,    in 
stepped  courses,   similar  to  Fig.    If.    In  designs  of  this  "class  the    sprees   between 
-ihe   timbers   always   should  be   filled  completely  with  clay,   gravel   or  core  rets, 
'Ise   the    sticks  should  be  bolted  or  drift  spiked  thoroughly  together.    This   type 
'f  construction  is   in  great  part  now  being  superceded    r;    the  use  of  reinforced 
oncrete  slabs  capped  over  the  heads   of  wooden  pilot,    I.  hsed,    in  some  designs 


72 

not  only  the  wooden  grillage  layers  but  also  the  wood  piles  are  being  replaced 

with  reinforced  concrete w ork.  On  the  filled  ground  areas  of  San  Francisco  timber 
grillage  on  piles  has  been  frequently  used  for  two 'and  three  story  CJass  C  brick 
buildings.  For  lighter  structures  piles  have  been  dispensed  with;  the  footings 
having  been  based  on  timber  rafts  of  open  layers  like  Fig.  24,  or  of  solid  layers 
of  12  x  12  inch  redwood  or  Oregon  pine  sticks.  Y/here  such  construction  h£.s  been 
permanently  under  tide  water  the  wood  has  remained  in  first  class  condition 
after  a  lapse  of  40  to  50  years,  and  no  doubt  would  remain  sound  indefinitely. 

Timber  under  these  circumstances  should r  always  be  placed  at  depths  below  the 

i 

lowest  possible  ground  water  plane.  As  a  city  grows,  its  surface b ecomos  more 
impervious  and  its  improved  sewers  and  drains  lower  the  water  table,  thus  some- 
times exposing  timber  which  was  not  placed  in  a  sufficiently  deep  excavation,, 

4.  INVERTED  APCKES  OF  STOHE,  .BRICK,  CONCRETE  OR 
~  REIKFOECSD  CONCRETE. 

Fig.  25  shows  a  typicsl  example  of  an  inverted  arch  footing.  These 
/ 

arches  frequently  are  built  under  and  between  the  bases  of  piers.  Employed  in  this 
way,  they  distribute  the  load  from  the  piers  A  and  B  over  a  greater  area,  and 
therefore  in  soft  material  make  shallower  foundations  possible.  For  light  loads 
the  arch  dimensions  maybe  assigned  from  experience,  or  where  >the  span  and  load- 
ing are  considerable,  the  r  ing  maybe  designed  by  applying  arch  analysis;  but  in 
the  case  of  the  inverted  aivh,  the  loads  are  applied  from  below  and  the  reactions 
et  the  ends  are  induced  from  above  by t heweignt  on  the  piers.  In  the  best  designs 
the  allies  rest  upon  a  bed  of  concrete-  of  considerable  thickness,  thereby 
insuring  a  thorough  distribution  of  the  pressure  froiii  below  upon  the  arch  ring, 
Care  .mist  be  taken  to  provide  for  the  end  arch  thrusts  at  outside  piers.  It  is 
assumed  that  the  pressure  from  below  on  the  surface  CJ)  is  uniform.  The  weight  of 
the  arch  ring  end  footi-ng  concrete  is  not  considered  as  an  arch  load,  since  it 
rests  directly  upon  the  foundation  bed.  The  total  load  on  CD  is  tie  sum  of  the 
ring  and  footing  weights  together  with  the  total  loads  upon  the  piers  A  and  B; 
this  toial  load  aiust  not  exceed  the  safe  bearing  capacity  of  the  soil.  The  arch 


73 

ring  is   cojnmonly  of  brick,    it  may  consist   of  concrete   or  stone   block  masonry. 
Since   the   advent  of  reinforced  concrete  more  slender   archers   of  reinforced  concrete 

t 

are  possible.    It   is  more  usual  liov.'evcr   to  dispense  w  it*,-  the  crch  '.principle  and 
employ  instead  distributing'  slabs  of r einf orced  concrete  acting  as  simple  or 
continuous  beams  between  the  pic  r  footings;   s<|     group  6,      The   construction  of 
inverted  arches   is  difficult.  Arches   of  brick  or  stone  blocks  a  re  now  seldom^  used. 
The  pressure  on  the  bed  CD  is  rarely  uniform.     Moreover  even  slight  uneven  settle- 
ment  is  especially  injurious  to  an  arch  construction.  , 

The  Droxel  Building,  Philadelphia,  and  the  ';;orld  Builfiing,  Hew 
Tork,  are  among  the  earliestof  the  steel  office  buildings,  Where  columns  were 
supported  on  inverted  arches.  Sec-  Eng.  Record,  Vol.  57,  Apr.  4,1908,  p.  414. 

Shallow  foundations  using  inverted  arches  should  not   be  built  upon 
filled  ground  likely  to    settle   or  upon  filled  ground  liable  to  nerve    from  earth- 
quake vibration  and  swash.   Instead,   concrete  slab  and  girder   footings,   hecvily 
I  reinforced,    should  be  used.    In  San  Francisco,   on  filled  ground,  v/here  two  and 
three   story  brick  buildings  had  their  walls  supported  upon  reinforced c oncrete 
slabs  at    shallow  depths 4  under  earthquake  motions   the  we  11s  settled  while  the 
basement   floor  slcbswere   forced  upward  at  the   center  line  b  etv/een  walls.    In 
t  one   case   the  max.   relative  vortical  motion  was  not  less  than  4   ft.   These   slabs 

."ere  ruptured,    even  when  considerably  reinforced.   Under  such  action  a  brick 

' 

inverted  arch  would  fail  utterly.  Arches  cannot  withstand  earthquake  shock.   Their 

oystones  are  easily  dislodged.  On  treacherous  ground  in  earthcucko  regions  even 
ooting  slabs  should  never  be  at  shallow  depths.  In  doubtful  cases  good  judgment 
.ill  select  a  pilo  foundation, 

5.    FOOTIIoU-S   OF  S  TJUCTUFJi.^  3TELL  BIL-.:i£  AND   CONGESTS 
Important   shallow  foundations  for  he,  vy  loads  on  interior   building 
Lumns   or  outer  walls  are  frequently  c  onstructed   of  grillages   of  steel  I -beams 
jedded  inconcrete,    THIs  method  was   first  used  in  Chicago,   using  railroad  rails 
stead  of  I-beams.    Fig.    26  illustrates  a  typical  caso.  The  base   of  the  footing 


.      74 
consists  of  a-heavy  slab  of  concrete,    1  to  2   ft.   or  more   t",:iclc  to  insure  cs  nearly 

as  possible  uniform  pressure   distribution  upon  tha   foundation  bed.   Upon  this  base 
are  placed  layers  of  I-beams  at  right  angles,  'each  tier  in  order  smaller  in  plan 
than  the   one  immediately  b  Glow  it.   The  beams  arc-   spaced  with  at  least  a  three 

• 

inch  flange  clearance  to  a  How  for  the  ramming  of  concrete  into   the  spaces  b  etween 
the  b  earns. 

Let  U  be  the   total  load  that  rests  upon  the  base   of  the  footing. 
Assume  that  this-  same  weight  rests  also  upon  each  tier  of  b  earns  and   that  it  is 
uniformly  distributed  over  each  tier.    Thos'e  assumptions   are  not  absolutely 
correct  but  their  orror  is  a  Iways  upon  t  he  side   of  safety.   Let  the  plan  of  the 
column  base  bo,  a  x  b;   that   of  the  first  tier  of  beams  below  it,   bj  x  1-p   that  of 
the  next  lower  tier  bg  x  12,   and   so  on;    in  other  words,    let  the   dimensions  of  the 
nth  tier  from  the  top  be  bn  x  ln-     Notice  that  a  =  bj,!1  =  bg,   lg  =     1>3,  etc.  and 
^•n  =  b  n-t-1-      The  concrete   bed  b4  x  14  must  be  proportioned  so  that  W  =  pb£l4 
inhere  p  is  the  allowable   safe  pressure  upon  the  soil.   In  Chicago  p  ranges    from 
3000   to  4000  Ibs.   per  sq.    ft.    It   is   important  to  provide  a  stiff  footing,    that   is 
one  that  will  not  tend  to  deflect.     Deflection  prevents  a  uniform  distribution 
of  the   load  upon   the  bed.    Consecuently  the    steel   offsets  must  ncc  be  too  great. 
It   is  better  to  use  deep  I-beams.   The  depth  D  should  not   be   too  small  compared 
to  b     and  14. 

In  Fig.   28  the  half  section  of  the   thrrd  and  fourth  tiers  of  Fig. 
26   is  shown.    The   lords  W/2   from  the  assumption  of  uniformity  of  pressure 
I/istribution  are  concentrated  at   the   center  points  A  and  B  of  the  respective  half 
tiers.   The  maximum  bending  moment  %  in  the   fourth  tier  then  obviously  becomes: 


%  =  Wn     =  W  {14  -  b£  )    =  W     (!4-b3)   =  V7   (14   - 

22448  8 

similarly  for  the   third  tier: 


1L   =  W  (13   - 

6        8 


r   in  general  for  the  nth  tier: 

Mn  =  W  (ln  -  ln_2)    ft.    Ibs.    =  3W 
8  2 


75 

In  equation  23  the  values  of  1  are  in  feet.  In  general  M  =  kl/d  ~ 
KR,  where  k  is  the  max*  •  allowable  fiber  stress  intensity,  I  =  the  moment  of 
inertia,  R  =  the  moment  of  resistance  or  section  modulus  c.nd  d  =  the  distance  to 
the  most  fibres  from  the  neutral  axis  of  a  tier  of  beams;  honcc:- 

Mn  =  3W  (ln  -  1  J  *  MkB  ........  ...............  (24) 

—       n-6 

In   equation  (24)      H  ?  the  number  of  beams'  in  any  tier,  k  =  577     (  1     -  ln  2)   and 

2KB 
H  =  3W     (In  -.1        )    ................    .=•*.;   ......    .    .    (25) 

2kR 

..........    ........    .  %    ......    ...    {26) 


n 

3W 

-'  In  general,  for  the  lowest  course  14  is  fixed  by  dividing  the 

ret  aired  area  by  b4  for  any  c  ourse  K  is  limited  by  the  length  of  the  overlying 
course. 

0 

Example   -  Steel   Grillage  Footing.      Let  W  =  800,000  lb.;  p  =2  tons 
=  4000  lb.    per   sq.    ft.    of  bed;  k  =  15,000  lb.   per  sq.    in.  px  =  350  lb.   per  sq. 
in.    =  allowable  pressure  between  cast   iron  base  end  first  tier  of  beams. 

The  cast   iron  base  area  a  x  b  =  800,000     _  =  16  sq.    ft.;   choose  a 

350  x  144 
sq.  base  4x4   ft.,  assuming  W  to  bo  the  total   load  on  foundation,  bed  for  an 

interior  column  for  a  high  building;   a  -  b  =4   ft. 

For  the  first  tier  of  beams   li  =  b  +  2JikR/3W.    Select  15  inch  42  lb 

.' 
I-teeams;   R  =  58.9,    flange  width  =  5.5   inches.   Hence  K   for  width  bj,  =  43  inches, 

/ 

is  48/  5.5  -••  3  =  about   6,    for  3  inch  clearance  of  flanges.    Then  lj  e 

1-   +  2  x  6  x  15000  x   58.9      =4+4.4   =  8.4   ft. 
3  x  800,000 

For    second  tier,    12  beams  with  5.5  inch  fl^ige  width  and  3  inch 

:learance,  gives  b2   =  ll  =  8.5  x  11   +  5.5  =  99   inches  *=  8.25   ft.   This   is  sfufficient- 
-vclose  to   the  preceding  value,   8.4  ft.   to  settle   too  selection  of    12  -  15"  42# 

.        '  N 

:--beams  for  the  second  tier,  using  a  spacing  nearly  3  itches.  Then 

T-2  =  a  +  2HkR_  •  4  +  2  x  12  x  15000  x  58.9  =  4  +  8.6  =  12.8  ft. 
3W          3  x  800  000 
For  a  third  tier,  18  -  15"  42#  I-beams  provide  a  reasonable  solution 

Disregarding  for  a  moment  the  necessary  dimensions  for  base  area  of  concrete' 

joting  slab  on  foundation  b  ad.  For  N  =  18,  13  =  !.,+  2  x  18  x  15000  x  58.9  = 

3  x  800  000 


8.4  +  13.2  =  21.6   ft. 

/ 

The  required  area  of  concrete   baso  bg  x  lg  =  1^  x  lg  =  V//p  = 

800,000/4000  *  ?*  0  sq.    ft.;  hence  1_  =  200/12.8  =  15.3   ft.   Consequently  the   baams 

o 

in  the  third  tier  maybe  shcr  toned  from  21.6  to   15.3  ft.   and  the  number  required 

is  N  =  5  x  800,000   (15.3  -  8.41  =  10  beams,  with  ;;  roster  spacing  than   3  inches. 

2  x  15  000  x  58.9 
Otherwise  a  lighter  boas,    say  12  inch  31.5  #  should  be  used,  saving  3  inches  depth 

of  foundation.1 

For  the  final  dimensions  fractional   lengths  should  not  bo  used. 
Thus  we  might  finally  select: 

Cast  iron  baso,  4x4  ft. 
Tier  1,  4  x  8.5  ft.  ..   6  -  15"  42#  I-beams 
Tier  2,   8.5  x  13   ft.,   12  -  15"  42£  I-beams 
Tier  3,   13  x  15.5  ft.,   10  -  15"  42£  I-bca.ns. 

For  acolumn  a. square  plan  is  desirable;   the  concrete   base  requires 
an  area  of  200  sq.    ft.    =  14  x  14   ft.   The  stool  beams  of  tier  3  neod  not  hevc  a 
3lan  greater  than  13  x  13   ft.    giving  a  concrete  base   6  inches  larger  s.ll  around, 
lake  the  concrete  be.sc   12   inches  thick.   The  stool  for   tier  3  should  be  redesigned 
Tor  plan,    13  x  13   ft.,    selecting  10  or  12   inch  i's.   For  an  additional  oxamplo 
portraying  this  method,   see  Eng.  Record,  Mar.  3,    1894,   p.   223. 

CAST  IRON  BASES,    STEEL  rZDESTALS,    etc. 

For  buildings,    column  bases  usually  arc  constructed  of  cast  iron; 
sec  area  a  x  b,   of  Fig.   26.    Fig.    27  exhibits   one   of  tho    erst  iron  bases  used,  in 
the  White  House,    1907,   a  largo  Department  Store  building  in  S?.n  Francisco. 

Fig.   27A  illustrates  an  interior  footing,  founded  on  sand,    in  a 
;iass  A  San  Francisco  Hotel  Building.   The  total   load  =  468.000  Ibs;    bod  aroa  = 
iO  sq.    ft.;    soil  pressure  =  3.9  tons  per  sq .   ft.;   cast  iron  base   =  3'6"   square  = 
L  ;.2  3q.    ft.;  pressure  under  cast   iron  base   =  265  lb.  -or  sq.    in.    The  student 
-.ould  calculate   the  punching  shear,  concrete  compression  end  rod  tension  in  the 
ooting  b-  methods   illustrated  in  the  next  article. 

Fig.    27B  exhibits  a  cast  iron  baso   for  a  wall  column  in  the  same 
tructure  as  Fife.    27A,    The  base   is  eccentric  because   of  the  nearness  of  the 


77 
structural  column  to  the  party  lino.   Eccontricity  of  bases,  e.s   of  footings 

tinder  thorn,   should  bo  avoided  whenever  possible.    The  total   load  on  this   base  is 
380,000   Ibs.    =  298   Ibs.   por   so.    in.    of  bod.     ' 

0 

Large  manufacturers  publish  standards  for  cast  iron  bases;  their 
handbooks  give  tables  of  standard  d otai Is,  dimensions,  weight,  bearing  capacity, 
etc.;  consult  American  Bridge  Co.,  Standards  for  Detailing;  Table  4  is  reproduced 
from  the  leaflets  of  the  Illinois  Steel  Co.,  1905. 

For  heavy  buildings  and  bridges,  cast  stool  is  sometimes  used 

instead  of  cast  iron.  Very  largo  pedestals,  particularly  for  trusses,  are  designed 
of  built-up  structural  shapes.  Fig.  27C  is  taken  from  Eng.  Record,  Vol.  65,  May  4 
1912,  p.  504,  and  illustrates  a  base  built  of  rolled  shapes  used  by  E.  W.  Stern 
for  buildings.  The  beams  per  layer  are  bolted  together  in  the  shop  including 
separators,  and  the  two  layers  of  b  cams  likewise  are  bolted  together,  all  ready 
for  erection  in  one  piece.  LIr.  Stern  advances  four  reasons  why  this  type  of  baso 
might  replace  cast  iron;  which  read. 

OTHER  DESIGN  METHODS  FCR  STEEL  GRILLAGE  FPOTIKGS. 

Equations  21  to  23  give  the  max.  bending  moment  in  any  tier  pro- 
vided that  the  deflections  of  the  different  tiers  do  not  affect  materially  the 
assumption  of  uniform  distribution  of  load.  These  max.  bo-ding  moments  occur  ct 
the  center  sections;  ifor  example,  at  C  for  tier  4,  Fig.  28. 

In  Fig.  28  lot  y  =  14/2  -  b3/2  =  the  projection  for  the-  beams  of 
the  fourth  tier.  Let  D  be  any  section  in  the  fourth  tier  within  tho  boundary  E 
of  the  next  upper  layer.  Section  D  is  a  variable  distance  x  from'E;  x  may  vary 
from  zero  to.  b.g/2.   The  intensity  of  uniform  load  acting  downward  upon  tier  4 
from  E  to  C  is  pi  =  V//b3 ;  that  below  tier  4,  acting  upward,  from  F  to  C  is  p2 
W/14-   The  bending  moment  M  at  D  is: 

M  =  P2/2  (y  *  x)2  -  Plx2/2 •  • •  •  •  • 

The   first  derivative  of  M  with  respect  to  x  is: 

.    dM/dx  =   (p2   -  »!)x   +  p2Y   •    •    •    • 
"Placing  tho  second  member  of  (29)    equal  to   zero  r.nd  solving  for  x  gives, 


-if.    :;' 


.•j,(!  ''  ' 


78 

-p1  =  v/y  =  b3/2 (30) 

-  W/b3) 


Therefore  the  ;nax.    valuo   of  M 'occurs  at   tho  center  section  C  = 
Placing  x  =  b3/2   in  equation  28, 

Me   =  W/8(l4-b3)   =  W/8   (14   -  12)    =  Wy/4    ........ (31) 

Equation  31  is  identical  with  equation  21. 

A  more  approximate  method  in  general  use  'calculates  the  bending 

moment  at  E,  Fig.  28,  assuming  uniform  loading,  and  considers  that  bending  as  the 
maximum'.   Thus  !%  =  p2y2/2  =  W/8  (U  -  1?.)£.  .  *  =  NkR  .  .  .  .  . (32') 

In  the  numerical  example  given  above,  considering  tier  2,  equation 

21  gives  M2  =  800,000  (13-4) /8  =  900,000  ft.  Ibs.j  oouation  32  gives  M2 • - 

2 
300,000  (13-4 )/  8  x  13  =  625,000  ft.  Ibs.,  a  value  only  70$  as  large.  Obviously 

the  approximate  method  produces  a  more  economic  but  less  conservative  design. 
Consult  a  contribution  with  insert  sheet  in  Eng.  News,  Vol.  26V  p.  116,  Aug.  8, 
i89l.  In  this  article  :ir.  C.  T.  Purdy  outlines  methods  for  design  of  Steel  beam 
footings  in  Chicago.  Sec  also  discussion  of  .Mr.  Purdy's  methods,  Eng.  Kovvs, 
Vol. -26,  pp.  312,  265,  415. 

The  analysis,  equations  (21)  -  (26)  isnot  the  most  accurate, 
because,  except  for  the  lowest  tier,  the  load  is 'not  uniform.  The  bending  of 
ihe  steel  beams  in  any  c  oursc  throws  a  greater  lor.d  on  the  two  outside  beams  of 
the  course  next  above.  A  more  accurate  solution,  producing  a  considerable  saving 
if  materiel  is  effected  by  applying  in  important  cases  the  more  exact  theory  for 
iontinuous  girders.  It  is  eucstionablc  however  whether  one  is  warranted  in  ,-naking 
:  \e  more  involved  calculations.  In  practice,  the  simpler  form  of  aquations  21  to 
)  justifies  their  use,  particularly  when  due  consideration  is  given  to  s.  rational 
lection  of  values  for  working  stresses.  For  a  mathematical  treatment  of  footing 
ress'-s,  assuming  the  beams  in  eny  tier  as  constrained,  sec  a^  scries  of  articles 
r  ilr.  £,  B.  Durand,  Eng.  Record,  Vol.  39,  1899,  pp.333,  354,  383,  and  407. 


•:;<. 


79 

6.    FOOTINGS  OF  REINFORCED  COI-jGliETE 


Footings   of  I-beams  or  rails  laid  in  concrete  have  boon  in  common 
practice   since  1890.  Recently  alternative  designs  of  reinforced  concrete  have  come 
into  use.   In  the   latter  typo  the  concrete  slab  is  reinforced  with  rods,    cither 
plain  or  deformed.   Usually  the    footing  consists  of  one  concrete   layer  beneath  the 
cast   iron  column  base,    Fig.  2?a.   This   layer  generally  has  only  one   set   of  bars  when 
the    footing  supports  a  vail  column,   the  bars  running  at  right  angles  to  the  l~ngtfc 
of   the  wall.    For  footings  under  interior  columns  the  slab  in  most  cases   is   square, 
reinforced  by  two  sets  of  bars  at  right  angles.  , 

VZA.LL  FOOTINGS  ' 

Fig.  29  gives  the  details   of  design  for  a  wall  column,   Boalt'Hall, 
University  of  California.  The   outer  walls   of  the   building  consist  of  concrete- 
faced  with  granite   and  arc   self  supporting.   The  stcelcolumn  carries  only  the 
dead  and  live  leads,   Pc   for   floors  and  roof  =  189,000  Ibs.    The   footing  plan 
GHJK  is   10  x  10  ft.    =  100  sr.    ft.;   it  carries   10  lineal   ft.  CDFE  of  wall  load. 
Between  columns  the  wall   loads  arc  carried  by  a  footing  4  ft.    wide.  Allowing   for 
window  openings,   the   total  wall  load   on  GHJK  is  Pw  =  238,000  Ibs.   The  slab 
GHJK  rests  directly  upcn    the   soil,   which  is    sandy  clay.   It  vail  be  noted  that 
the  column  axis  aa  is   eccentric  a  distance  n,  while    the  w  a  11  center  lino  bb  is 
acentric  m  inches  to  the   other  side   of  the   footing  center  line  AB.    The  resultant 
load  P  =  Pc   +  PW  =  427,000  Ibs,,  m  +•  n  by  design  for  all  wall  columns   in  the 
building  was  taken  equal  to   10  inches;   again  JV/  (m+n)   =  P*1;  hence, 

n  =  Py;(m»n)      =  258,000  x  10  =  5.6  inches,     m  =  10  -  5.6  =  4.4   ins. 
P  427,000 

BEARING.   The  axis  aa  for   columns  was   fixed  4  ft.    6.5  ins.    from  the 
.'tmcr  side  GH  of  the  footing;   consequently  the  lino   of  the   force  P  lies  4  ft. 
3.5     ins.    -i-  5.6  ins,    =   5   ft.   0.1   ins.    from  that  edge.    For  practice.!  purposes 
'•'horeforo  it  may  b  o  assumed  that  the  resultant  lead  P  is  central  upon  d&JK  and 
'hat  it  acts   in  the   line  AB.   The  pressure   on  the  bod  is  uniform,   its   intensity 
=  427,000/100   =  4270  Ibs.    per   so.    ft.    =  2.15   tons.  A  pressure   of  2   to  2,3   tons 


per  sq.    ft.  was  tentatively  assigned   for  the    foundation  bod  throughout  the 
building  plan.  « 

SHLAR.      The  footing  depth  was    taken  equal'  to  36  inches, with  roin- 

t 

forcement  bars   6  ins.    from  the  bottom  surface.    The    shear   oxortoc.  by  the  wall 
load  acts  on  the  vertical   sections  CD  and  EF;   their  combined  area  =  2  x  10  x  3  = 
60  sq.ft.;  hence  neglecting  the  stiffness  offered  by  tho  bars,  the  shear  applied 
to  the  concrete  =  427,000/60  =  7100"   Ibs.  per  so.    ft.    =  50  Ib.   per  sq.   in.   This   is 

a  c onservatiVe  calculation;   tho  shear  is   below  safo  working  values    (100  Ib.  per 

I 

sq.  in. )  for  concrete.  Observe  that  it  is  hero  assumed  that  the  wall  CDFE  dis- 

\  * 

tributes  the  column  load  upon  the  sections  CD  and  EF. 

BEEPING,   DESIGN  FOR  REINFORCEMENT  , 

Considering  simple   cantilever  action,   tho  ..lax.    bending  moment  in 

\    • 

the  slab,  by  equation  (23).,  roughly  is: 

M  =  427,000.     (    10_  -_3)    =  375,000   ft.    Ibs.    =  4,480,000   in,    Ibs. 

2  44 

Tho   gross  depth  of  slab  D  -  36  inches;   effective  depth  from  stool 

bars  to  top  surface   of  concrete,   d  =  30  ins.      For  approximate  calculations  k  =  0.4 

and  j   =  0.86;  consult  Turneauro  &  Maurer's  Principles  of  Reinforced  Concrete. 

i 

Unless    otherwise  stated,    those   values    for  k  and  j  will  be  used  in  what  follows 
whenever  calculations  for  reinforced  concrete  beams   ETC  made.   Foundation  loads 
cannot  be  a ssi gnod  accurately;  usually  the  beams  are    short  and   thick  and  do  not 
satisfy  closely  the  common  theory  of   flexure,    or  they  arc  constrained  as  con- 
tinuous spcvns   or  act  partially  as   slabs  supported  on  four  edges.   Tho  bending 
moment  M  therefore  is  not  a  certain  value;  approximate  calculations  are  justified, 
Similar  remarks  apply  to  investigations    for  shear,  kd  =  30  x  0.4  =  12,    ins;   jd  = 

0.86  x  30   =  25.8   ins,;   F  =  4, '480, 000/25. 8   =  173,000   Ibs.    *  total   fiber  stress   on 

* 
stool  tars   in  tension  and  on  concrete  in  compression;   fs  =  allowable   intensity 

of  stress   in  steel   =  16,000  Ib.  per  so.    in.;  As  =  necessary c ross    sectional  area 
of  steel  bars   =  173,000/16,000   =  10.8  sr .    ins.;   use  therefore  21   -  3/4   in.    sq. 
bars,     9    ft.   long,   spaced  r.bout  5  3/4"  ccntors.  At  rijht  c.nglcs  to  this  group 
of  bars  place,  as   shown  in  Fig.   29 ,  4  -  3/4"   sq.   bars  to   stiffen  the  slab  and 


81 

hold  tho  other  bars.   The  neutral   surface  is   approximately  kd  =  12  ins.,  below 
the  top  surface   of  concrete;   therefore  the   concrete  cross  section  subjected  to 
compressivc   fiber  stresses   is  AC  =  10  x  12  x  12  =  1440  so.    ins.     Upon  this  area 
tho    stresses   vr.ry  linorrly  from  zero  to  a  maximum;  hence  the  uiaximum  concrete 
comprossion=fc  =  2F/Ac   =  2  z  172,000/1440  =  240  Ibs.  per  so.    in.      fc  might  safely 
be  400  to   500  lbs=   por  s  q.    in.,  which  shcv;s  that  tho    footing  slr.b  is  conservatively 
thick  for  bonding,   but   it   is  not   too  thick  in  shear. 

INTERIOR  COLUIflT   FOOTINGS 
Fig.   30  show  s  details  for  an  interior  column,   Boalt  Hall,  University 

of  California. 

t 

BEARING.    The    footing  is   square   in  plan,   8  x  8   ft. ,    it  is  36  in. 
tMck  with  steel   6  ins.    from  tho  bottom.   The   total  load  P  =  275,000  Ib.   The 
intensity  of  pressure   on  the  bod  =  p  =  275, QOO/  8x8=  4300   Ib.    -  2.15  tons  per 
so.    ft. 

SHEAR.      The  cast   iron  base   has  a  plan   =  30  x  39      ins.   honco   tho 
total  arod  $f  shearing  section  ABCD  =  4  x  39  x  36  =  5600  sq.   ins.,   shear  inten- 
sity not  considering  effect  on  bars   =  275,000/5600  =  49   Ib.  per  sq.    in. 

BEHDIKCr.  An  approximate  method  for  calculations  will  bo  used; 

consult  Designing  Ilcthods,  Reinforced  Core  rote  Construction,   Expanded  I.Iotal  and 
3orrugatcd  Bar  Co.,   Vol.    1,  Ko.   2,    June  1908,  p.  49.    Two  sets   of  bars  at  right 
.ngles  are   employed.   Tho  upward  prcs&uro   on  triangle  EOF  and  the  downward,  pressure 
m  DOC  are  each  equal   to   1/4  of  P  or  to  69,000  Ibs.   The  max.    bending  M  is   in  the 
cortical  plane  XY;  G  is   the  controid  of  triangle  DOC,   H  that   of  EOF;    OG  =  1/3 
•f  AD  -   13  ins. ,   OH  =  2/3   of  XE  =  32   ins. ;   honco  M  =  Pm/4  =  69000  x  19   = 
.,310,000  in.    Ibs.    This  moment   is  resisted  mainly  by  the  concrete  and  bars  below 
id  within  tho  confines  of  the   cast   iron  base.    Of  course   only  bars  normal  to 
T  can  be  considered,  and  of  these  bars,  those  that  arc  near  the  lines  XE  and  YF 

little  work.  Assume  that  11  is  resisted  in  the  vortical  plane   through  XY  by  the 

' 
•ncrote  and  bars  in  a  width  equal  to  a  side  DC   of  the  column  base  plus  -the  depth 

•f  footing;    thus  the   available  width  w  =  39   +  36  =   75  ins.   The  distance  EF  is 

' 


82 

96  Ins.,   not  greatly  exceeding  w,  but  this  is  due    to   the  fact  that  the    footing 
depth  of  36  ins.   has  boon  assumed  generously.   The  bending  moment  per  ft,  width 
is  MI   =  M/w  =  1,310,000/  6.25  =  210,000   in.    Ibs.,   B  =  36   ins.,   d  =  30   ins,, 
kd  =   12   ins.,    jd  =  25.8  ins.,   hence   F  =  210,000/25.8   =  8140   Ibs.;    fg   =  16,000  Ib. 
por  sq.    in.,  AS  =  0.51  so.    ins.;   use   1/2   in.    square  bars,   7   ft.   long,   spcccd  6 
ins.   centers  in  two  groups  at  right  angles. 

&ENERAL  COMMENT  ON  THE  DESIC-IT  OF  FOQTIKuS  UEDSR  INTERIOR  COLUMNS 

The  problem  of   the   design  of  square  of  rectangular  footings, 

reinforced  in  two  directions,   is    similar  to   that   for  floor  panels   in  which  the 
slabs  rest   on  all    four  cdgos.    For  ordinary  soiJLs  the   allowable    footing  pressures 
range  from  2  to  4   tons  or  4000  to  8000  Ibs.  per s q.    ft.    Floors  usually  carry  a 
total  load,  dead  and  live,    of,  only  200  to  500   Ibs.   per  so.    ft.    of   floor  slab. 
Hence  footing  slabs  are  much  thicker;    in  their  beam  action  they  are   short   in 
span  and  deep   in  section  ssfi  require  special  attention  to  provide  against  excess- 
ive  shear  and  bond  stresses. 

It  is  difficult  to   calculate  accurately  the   stroscos   in  a  square 
footing.  Assumptions  have-  been  made    in  the  design,  Fig.   30,  which  give   results 
well  on  tho  side   of  safety.   For  more   exact  analyses,  tho  theory  of  stress   in 
square  an4  circular  plates  may  bo  applied  to  this  problem.    See  Principles  of 
Reinforced  Concrete  Construction  by  Turneannc  &  Mauror,   3d  od. ,   1919,   Chap,    8; 
also  an  article  by  Prof.   H.  T.    Sdcy,   Year  Book,   Lngincors  bocioty,  University  of 
Minnesota,   1899. 

Tho   following  gives  mother  treatment.   As  a  general  principle  the 
pressures  should  be  carried  as  directly  as  possible   from  the  edges  ABCD,   Fig.    31, 
to  the    center.   The   square  EF&E 'represents  the  plan  of  the   cast   iron  column  base, 
'Jwo    sgts   of  main  reinforcing  rods   aa1   and  bb1   within  tho   limits  shown,  will  do 
oho  most  work.   To  reinforce  tho    corners   the   two  sets   of  diagonal   bars  dd1   arc 
introduced.    In  footings   of  large  plan  ABCD  ard  relatively  snail  column  base  EFC-H 
chc  groups   of   bars  aa1  ,   bb'   and  dd1   will  not   cover  the   entire  area.    'Triangular 
.  -    Hire  J::L  arc1    loft.    To   offset  this  a   fc*  short 


83 

The  criticism  to  be  .tado  of  this   scheme   of r cinforccm&nt  is  that 
it  uses  considerable   steel  and  congests   it  under  the  column  base.    In  making 
calculations,   the  total  pressure  on  BFGC   is  assumed  to  bo  carried  to  the  vertical 
section  at  PG  whore  the  bonding  moment  and  shear  are  maxima  and  may  be   studied 
as  in  the  preceding  problem,   Fig.    30. 

The  max.   shear  and  diagonal  tension  in  footings  ere   found  near 

section  QR,   Fig.   31.   Cracks  tend   to  occur  along  the  curved  linos  oc1.   Bent  rods, 
when  used,   must  be   bent  up  as  shown  just  outside  the   column  base.   They  aro  net 

needed  near  the  end  of  the   beam.   Stirrups,  g,  must  be  spaced  closely  near  QR  but 

r 

can  be  omitted  further  out. 

For  economy  large  footing  slabs  may  be  increased  in  thickness  pro- 
ceeding  from  the   outer  edges  toward  the  center,   Fig.   31A,   or   they  may  bo   stepped 
as   shown.  Again,  a  thin  footing  slab  maybe  used,  ribbed  on  the  under  sMo  with 
beams  of  greater  depth,  thus  securing  the  benefit  of  T-action,   as  in  floors. 
Tho  upward  pressure  from  the   foundation  bed  tends  to  pull  the   slab  away  from  the 
beam,,  but  the  use  of  sufficient   stirrups  properly  bonded  to  the  horizontal    steel 
bars   in  slab  and   beam  will  give  adequate  anchorage.   See  Turncaurc  and  Maurer, 
just  cited,  Chap.   9,    fig.   35,  p.    337.   Consult  Engineering  News,   Vol.   56, p. 30. 

g.   COIIBIITEP  FOOTINGS 

In  large  buildings    (class  A)   all  the   lords,   oven  of  the  walls,  arc 
supported  dir  :ctly  by  rows   of  regularly  placed  columns.    If  possible    tho    footings 
are  disposed  symmetrically  febout  tho  center  of  gravity  of  the   column  loads; 
usually  they  arc  squr.ro.    Frequently  c.n  exterior  column   footing  cannot  be  designed 
square,    because   of  the   limitations  to  tho   size   of  tho    lot.    In  such  a  case,  tho 
load  of  the  wall  column  may  be  connected  with  that   of  the   nearest   interior  column 
-jy  designing  a  special   trepezoidr.l   footing.    Sometimes  three   or  more  columns  may 

their  footing  combined  by  employing  cr.ntilcver  and   continuous   slabs.    In 
ildings   on  irregular  lots,   a  cluster  of  columns  at  a  corner  or  under  a  tower 
iay  be  supported  upon  a  large  polygorcl  slr.b.   Tho  main  principle  to  be  satisfied 


,TF-VO 

bua 


84 

of  gravity  of  the  combined  column  and  footing  loads;  sec  Chap.  3.  Combined 
footings  may  consist  of  stool  I-beams  embedded  in  concrete.;  such  designs  are  moat 
common  for  vory  hcrvy  foundations.  Or  they  may  b  o  off  reinforced  concrete  slabs, 
girders  and  beams  constituting  a  floor,  similar  to  a  building  floor,  but  reversed 
as  to  loads. 

Some-  heavy  footings  arc  monolithic  slabs 'covering  tho  entire 

building  plan.  This  typo  is  usual  for  tall  tower  like  structures.  See  Figs.  4A- 
4B;  Sather  Campanile  foundation,  whose  concrete  slab,  8  ft.  thick,  48  ft.  sq. 
in  plan,  is  stiffened  by  tv/o  layers  of  24"  I-beams  supported  upon  a  lower  4  ft. 
bod  of  reinforced  concrete. 

CALL  3WILDING,  SAN  FIO'CISCO.  Fig.  31A  shows  tho  base  of  the  Call 
building,  Sen  Francisco,  established  on  wot,  compact,  hard  sand,  in  natural 
place,  at  a  depth  of  about  25  ft.  9  ins.  below  the  street  level.  On  this  sand  was 
poured  a  bed  of  concrete  2  ft.  thick,  96  x  100  ft.  plan.  The  base  of  tho  build- 
ing at  the  sidewalk  level  is  75  ft.  square.  Upon  the  concrete  bod  rest  tv/o 
layers  of  15  inch  stool  I-bcams,  58  in  the  first  and  63  in  thc'second,  at  right 
angles,  forming  a  grillage  of  beams,  each  spliced  beam  about  96  ft.  long.  Those 
two  layers  are  covered  with  concrete.  Upon  the  grillage-  were  placed  28  sets  of 
20"  I-beams  to  carry  the  columns  and  pedestals.  The  cast  stc.l  pedestals  arc 
firmly  held  by  anchor  bars  extending  down  and  keyed  into  the  webs  of  tho  lower 
layer  of  15"  I-beams.  The  footing  therefore  is  a  great  table  of  reinforced  con- 
crete, 54  inches  thick,  giving  an  average  soil  pressure  4500  Ib.  per  sc.ft. 
The  superstructure  weighs  12000  tons. 

V/ASHIKSTOH  MONULENT ,  In  1878  the  monument,  Fig.  31B,  had  been 
completed  to  elevation  AB,  156  ft.  4  1/8  ins.  above  the  top  of  its  foundation 
CD.  The  mean  lengths  of  side  and  thickness  of  shell  at  AB  are  48  ft.  9  5/8  ins. 
and  11-  ft.  10  5/16  ins.;  at  CD,  55  ft.  1  1/2  ins.  and  15  ft.  1/4  ins.  The  shaft 
consists  of  white  nr.rblc  facing  and  bluest  one  backing/  The  original  foundation 
CDEF,  23  ft.  4  ins.  in  thickness,  of  blue  gneiss  rubble  masonry,  laid  in  pure 
lime  mortar,  was  carried  up  from  bottom  to  too  in  8  offsets  or  stops.  The  first 


85 

or  lowest  step  vizs  80'   x  80'  x  2'4"  riso;    the   oighth  or   top  stop,    58'6"  x  2*11" 
rise;   the   other  stpps  being  more  or  loss   in  proportion.   3y  rctual  experiment  the 
masonry  wcs  found  to  average  164.88  Ibs.  per  cu.    ft.    in  v/fcight 

The  w  eight  then  of  tho  partially  completed  shaft  was: 

weight   of  shaft  23  794  tons 

weight   of  foundation  8,139'" 

weight  of  earth  on  foundation  243  " 

total  32,176  tons 

This  weight  distributed  or  or  a  bed  6400  so.    ft.    in  area,  gave  a 

\ 

pressure   of  5.027  tons  per  sq.    ft,    of  2240  Ib.    each. 

In  1878  the  Corps  of  Engineers,   U.    S.  Array,  was  ordered  "to  prepare 

' 
a  project   for  strengthening  tho    foundation,   to  tho  ^nd  that    the  monument  may  be 

'  carried  to  a  height   of  at  least   525  ft.   above  the  present  top  of  the    foundation", 
For  this   new  height,  and  with  earth  filled  upon  the    foundation  to  level  CD  the 
total   load  on  tho  bed  EF  would  have  been- 

weight   of  shaft  43,421  tons 

woight  of  foundation  8,139  " 

weight  of  roof  and  stairs,   etc.  250  " 

weight  of  earth  on  foundation  2,283  " 

total  54,093  " 
< 

or  8.452  tons  per  sc.    ft.  'with  a  wind  pressure   of  55  Ib.   por  sq.    ft.  acting  on 
the   shaft's  vertical  projection  would  have  given  a  max.    of  9.941  tons  per  sc-ft, 

?-t  the   toe  of  bed  EF.  This  value  was  considered  unsafe. 

• 
The  substructure  was  undermined  by  sections  and  now  /masses  of 

Portland  cement  concrete  ;r£.sonry  introduced   in  thin   vertical  Icyors,  not   over 

<i   ft.    in  width,   having  first  tunneled  under   the   structure  with  drifts   of  that  ( 
I  \ 
.vidth  and  the.  required  height  and  length.   The  new  bed,   126' 6"  square  has   its 

•jvel  GH  at  the  water  lovol,    or  12 '4"   below  the   earlier  bottom  EF  of  the    first 
oundation.   The  new  masses  were  extended  18  ft.   under  the   outer  edge  of  the   old 
oundction  end  5  ft.   under  tho   outer    face  of  the  shaft  at   its  lowest  joint.   The 
>d  of  the   final   foundation,  with  the  oarth  terraced  to  the   Ic-vol  of  the  bottom 
f  the   shaft,    is  subjected  to   loads   as  follows: 


I-.- 


•'  '-  ' 


86 

weight   of  shaft  43,671  tons 

weight  of  foundations  21,160 

weight   of  earth  on  top  of  foundation  14,269 

.weight  of  earth  within  foundation  1.278 

total  80,378   tons 

giving  a  mean  pressure   of   5.022  tons  per   sq.    ft.;   or  a  re.::,   with  a  55  Ib.  wine,  of 
5.398  tons;  which  is   only  0.371  tons  greater  than  that  c::ertcd  by   the  partial 

* 

structure  upon  the  older  bed  EF. 

The  student  should  read  the  report  of  the  Chief  of  Lngineers,  Thos. 
Lincoln  Casey,  45th  Congress,  3rd  Session,  House  of  Representatives, ;,iis.  Doc.l\o. 
7,  8,  9,  etc.  for  detailed  accounts. 

SINGER  BUILDING  FOUNDATION.   Consult  Trans.  A.n.  Soc.  C,E.  ,  Vol.  63, 
p.  1,  particularly  fig.  12, p.  23.  At  the  basement  level  the  tower  is  60  ft.  square 

• 

center  to  center  of  columns;  the  CD  lumns  arc  12  ft.  on  centers;  6  columns  per 
side,  or  36  columns  total;  the  height  is  560  ft.  above  basement  to  base  of  lan- 
tern. The  greatest  depth  of  caisson  below  basement  is  73  ft.  or  92  ft.  below 
curb.  The  height  of  tower  from  bottom  of  caisson  to  top  of  flagpole  is  745  ft. 
The  lantern  is  66  ft.  in  height;  the  flagpole  40  ft. 

The  main  tower  then  is  a  square  prism  63  x  63  x  560  ft.  above  the 
basement  level.  The  weight  of  tower  is  18,365  tons.  The  height  of  the  main 
building  adjacent  to  the  tower  is  191  ft.  8  in.  from  sidewalk  to  roof.  Therefore 
it  was  assumed  that  wind  pressure  could  act  only  upon  the  upper  350  ft.  of  the 
tower.  Though  30  Ib.  per  so.  ft.  of  wind  pressure  was  proscribed,  in  the  cal- 
culations this  v,as  reduced  to  20  Ib.  on  account  of  a  50^  increase  allowed  by 
the  building  code  for  wind  stresses  when  compared  to  dead  and  live  lead  stresses. 
The  wind  force  on  the  exposed  tower  above  the  14th  story  then  is  \7  = 
=  442,000  Ib. 

Considering  the  tower  to  rest  on  a  base  70  x  72  ft.  the  average 
pressure  by  a  monolith  theory  is  18400/70  x  72  =  3.65  tons  per  sq.ft.  The  wind 
force  of  442,000  Ibs.  moves  the  center  of  pressure  4  ft.  from  the  center  of  the 
figure,  giving  E  range  of  pressures  from  2.4  on  the  windward  to  5  tons  per  sq. 
ft,  on  the  leeward  edge  of  the  base. 


87 

As  a  matter  of  fact  the  tower  rests  on  caissons  about  80  ft.    long. 
Those  caissons  wore  proportioned  to  t  alec  a  load  not  to  exceed  15  tons  per  sq.ft. 
Since  tho  wind  pressure  docsnot  exceed  50fb  of  the  dead  and  live  load,   it  was  net 
regarded  in  figuring  the   caisson  pressures.    It  was   considered  in  designing  tho 
steel  wind  f  ran  ing  ard  the  anchorage  of  columns  to  caissons 

TRAPEZOIDAL  COMBINED  FOOTIK3S 

Let  A  and  B,   Fig.    32,  be  loads  carried  by  columns  A  and  B;   x0  - 

the   distance  of  the  point   of  application  of  the  resultant  load  A+B  from  the  conter 
of  A;   m  =  distance  between  center  linos   of  colmrns  A  and  B.   Talcing  moments  about 

A:- 

Bm  =   (A  +  B)xQ;   hence  x0   =  Bm/  A+B  .....    .    .    .    ......    (33) 

The  combined   footing  acts   like  a  beam  resisting  tho  upward  pres- 
sure  of  the   soil.    It    is  supported  at  tho   ends  by  the  downward  column  leads.   By 
-  naking  the   center   of  gravity  of  the   footing  plan  coincide  with  the  resultant   of 
the  column  loads,  a  uniform  soil  -pressure   is  produced.  Strictly  this   ia  only  true 

* 

r/Lon  the  weight   Qf  the   footing  is  constant  per   sq.    ft.    of  plan;   that   is,  v/hon  tho 
footing  slcb  is    of  uniform  thickness. 

Let  p  =  the  allowable  soil  pressure,  P  =  tho  total  weight  of  footing 
and  k  =  tho  area  of  footing  plan;   then: 

k  =  P  +  A   +  B  .......    .    ......    .......    ^34) 

p 
Observe  that  since  the  column  loads  A  and  B  arc  resumed  unequal 

:;ho  footing  will  have  a  trapezoidal  shape;  if  A  =  B,  the  trapezoid  becomes  a 
cctanglo.  Let  a  and  b  be  tho  parallel  sides  of  tho  trapozoid.  If  A<B,  a<b 
ISD  .  Lot  1  =•  total  length  of  footing,  and  y  =  distance  from  center  of  wall  column 
to  tho  lot  line.  Note  that  XQ  is  determined  by  equation  (33)  while  y  is  given 
Torn  tho  study  of  the  ground  plan.  Hence  the  centroid  of  the  trapozoid  must  bo  a 
istance  x0+y  from  the  lot  line  at  column  A.  Usually  1  and  z  are  given  from  the 
around  plan  studies  also. 

(55) 


2 
Consider  tho  trapezoid  composed  of  a  rectangle  al  and  two  right 


88. 
angled  triangles;  take  static  moments  about  a.  point  in  the  side  a: 

Si?  (b  -  a)l3  =  k  (x0+y)  .  .  .  .  ........       ....   (36) 

2.     3 

In  practical  problems,    in  equations    (35)  and   (36)  all  quantities 

are  known  save  a  and  b;   solving  for   those  unknowns: 


b  =  2k  (3(x0+y)_i 
1  (   I 


a  =  2k/  1  -  b  .....  ...,..,.....;....,....   (38) 

If  B  =  2A  and  it  is  assumed  that  y=Z=0;l=m,  from  (33), 

X0  =  £!•"  from  (3?)  b  =  2k/l;  and  from  (38),  a  =  O/  Therefore  the  nethod  fa  Is 
3 

when  the  interior  column  load  is  tvo  or  more  times  that  of  the-  wall  column.  '  In 
such  cases  the  footing  must  bo  prolonged  beyond  column  B  into  the  lot  area.  Then 
the  sle.b  of  span  m  becomes  continuous'  with  a  cantilever  span  -projected  to  the 
tight  side  of  B.  Heavy  bending  is  produced  at  B.  Commonly  for  this  type  the  plan 
of  footing  bod.  is  made  rectangular.  The  foundation  slabs  maybe  designed  in 
reinforced  concrete  or  in  tiers  of  structural  stool  beams; 

With  "She  plan  dimensions  of  the  trapezoidr.l  footing,  determined  and 
its  thickness  D  assumed,  the  slab  should  be  designed  as  a  reinforced  concrete 
beam  of  span-  m  loaded  with  an  intensity  A+B/k  Ib.  per  so.  ft.  It  is  convenient 
to  consider  a  12"  width  of  beam,  mcr.suring  the  12"  horizontally  and  perpendicular 
to  m.  The  main  reinforcement  rods  should  run  parallel  to  the  line  AB  for  the  rods 

near  the  .median,  line  of  the  trapezoicl.  Proceeding  latcfr.lly  towerd  the  sides,  the 

f 
rods  should  diverge  slightly  so  that  the  outermost  ones  run  parallel  to  the  in- 

clined sides  of  the  trapezoid.  Particular  caution  should  be  observed  in  the  design 
of  inclined  bars  g  and  stirrups  h  for  the  webs  of  these  thick  slabs.  Bond  vrlues 
r.nd  anchorage  details  for  reinforcement  metal  should  be  studied  carefully  at  the 
column  ends  of  the  footing.  Observe  that  such  a  slab  must  be  considerably  con- 
strained at  its  ends.  Heavy  reverse  bonding  must  exist  under  the  columns.  The 
value  for  the  maximum  bending  moment  near  the  center  of  the  span  m  may  bo  grossly 
approximate  when  the  span  is  considered  simply  supported. 

Since  the  footing  hrs  considerable  width  at  its  ends  a  and  b,  it  is 


39 

necessary  to  distribute  the  colu/im  loads  laterally  by  placing  transverse  bars 
under  column  A  for  a  width  at  least  2y  and  under  column  B  for  a  width  of  2z.  Such 
reinforcement  is  to  be  calculated  as  for  square  footings;  see  Fig. 30.  There  is 
therefore  a  vertical  section  like  EF  at  column  A.  distant  about  2y  from  the  edge 

• 

a  of  the  trapozoid,   for  which  special  shear  calculations  should  be  made;   similarly 
for  a  corresponding  section  near  colujnn  B.   It  maybe   found  that  the  assumed  thick- 
ness D  of  slab   is  excessive  or  too  thin  to  give  required  strength;   then  proper 
changes  must  be  made,  which  in  turn  will  affect  the  v/eight  P,   thus  the   area  k, 
equation  (34).  A  second  calculation  should  readily  give  satisfactory  results.  Hotc 
that   the  load-    for  which  beam  stresses  are  calculated  in  the   slab  or  span  m  docs 
fiot  include  the  deadweight  P  of  tho    footing.   When  the  base   of  column  A  is   small 
it  maybe  that  tho  punching   shear  exdrted  around  its  edges  is  grocter  in  intensity 
than  that  along  the  lino  EF;  this  oc  cure  when  tho  length  of  tho  boundary  of  the 
cast  iron  base   is   loss  than  EF. 

Numerical  Example.      Soaring.    Suppose  column  A  carries  220  tons,   B 
300  tons.    Lot  the  working  pressure  under  cast  iron  colum»  bases  bo  350  Ib*  per 

sq.   in. ;   then  area  base  A  =  220  x  2000  =  8.75  sq.ft.;   similarly  area  base  B  =  11.9 

350  x  144 
sq.ft.  Use  square  plan  bases;    for  A  =  3  x  3   ft.,   for  B  =  3  1/2  x  3  1/2  ft.  Assign 

y  =  2  ft.  ,   z  =  2  ft.    6  in.    Suppose  m  =  12  ft.   Then  1  =  m  +  y  +  z  =  16  ft. 6  in. 
Consider  the   safe  soil  pressure  p  =  4  tons  per  s  q.    ft.  Neglecting  own  v/eight   of 

slab,   the   area  of  trapezoidal  footing  required  =  220  +  500  =  130  sq.ft.  Assume 

4 


the 


slab  4   ft.    thick;    its  approximate  weight  P  =  150  x  4  x  130  =  78,000  Ib. 


Kence  k,   equation  (34),    =  140  sq.ft.    By  equation  33,  x0  =  500  x  12  =  6.92  ft. 

520 
By  equation  37,  b  =  2  x  140   (5  x  8.92  -  1.)   =  10.55  ft.;   a  =  2  x  140  -  10.55  = 

16.5  16.5  16.5 

6.45  ft.   Practically  make  b  =  10  ft.    6  in.  ,   a  =  6  ft.    6  in. 

of    Sleb.   The  effective  upward  pressure  producing  bending  and 


shear   is  p'   «=  220   +  300     =  3.72  tons  =  7450  Ib.  per  sq.    ft.   For  a  strip  12   in. 

140 
wide  the  bending  moment   is  M  =  p'm2/12  -  7450  x  144/12  -  89,200  ft.lb.   < 

1,070,000   in.    Ibs.     D  *  48   ins,,   d  -  42  ins.  kd  -  16.8   ins.;   jd  =  36  ins  .    F  = 
1,070,000/36  -  29,700  Ibs.;   for  fs  =  16000  Ib.  per  sq.    in.,  As  -29700/16000 


:  sd  filtforfa  enoJ  telyol^o  tsorfa  Islotqe  riolrf 

'         »-  -L  - 

orfJ  J-'uW  Jbtii'ol:   scf  YS.T;  JI   .6  actfrloo  tsoa  rro 


t/pot  QV±T.  o,t  KirfiJ'  oo^.  1C  ovif; 


ft  aw?*   ,1  Jrf£iaw  tvf^  *oo'tl;JS  Iliv,1  /nu^  rti   Icjl'..'  ,.  *8i/o 

'•  '  •  • 

3  ovijk  v,iibsoT  br.corls  cioi?a£'  >s  A  .(Wil 

•";  -,  ,  .  i;r.^  ;v  !'"; 

.ic  cfafs   or!*  «i  6-otfEl.uol53  OTD  iaaao^c 

nmoloo  "io  eesd-  ori*  rto/^V  .£Cfiloa1   orf*  lo  b  c^It  ofc 


BVC 

:'   riOii. 

foo  :foif  »3iia   .  :;OT;  s.  ^ri*  i'oJ    .ancJ.  005 


V  .'- 

:..i   .$"$  S\I  5  x  Si\I  5*8  "JOl   ,  .it!   S  x  1 
'""ai  d  ft.  dl  »  s  *  Y  +  m  *  X  «t-rf?"  .*!  SI 


:r  000, 


o    ,?o  trei 


90 

sq.in.  ,  use   1  in.    sq.    bars  at  6  in.   centers;    fQ   =  2  x  29700     =  297  Ib.   por  sq. 

12  x  16.8 
in.      Since  the  concrete  could  stand  500  Ib.  per   so.    in.    the    slab  is   seon  to  be 

thicker  than  necessary  so  far  as  concrete   in  compression  is   concerned.    But  a  thinner 
slab  would  require  heavier  stool  bars.   Simple    calculations  would  determine  quickly 
the   economic   value   of  D  considering  fiber  s  tresses  alone.  A   study  of  shoai  and 
diagonal  tension  near  the  columns  may  show  that  D  =  4   ft.    is  desirable;   moreover 

| 

a  thick  stiff  slab  aasures  more  definitely  a  uniform  pressure  distribution  p1. 

Shear.  At  section  EF  the  shear  roughly  is  440,000  Ibs.  The  concrete 
section  =  7.5  x  4  -  30  sq.  ft.  Hence  neglecting  the  metal  reinforcement  the  average- 

shear  intensity  =  440,000  =  102  Ib.  per  sq.  in.  The  max.  shear  of  the  center  of 

30x144 
the  slabs'  depth  would  exceed  this  value  and  shows  that  D  was  not  taken  too  large., 

further,  that  v/eb  reinforcement  is  required.  It  is  to  Tap  supplied  in  the  form  of 
inclined  bars  and  stirrups,  but  the  computations  will  bo  omitted.  The  shear  area 
for  columnbaso  A  =  4  x  3  x  4  =  48  sq.ft.  which  shows  that  the  section  EF  in  this 
case  gives  the  greatest  web  stresses;  simit  r  remarks  apply  to  column  base  B, 
In  other  problems,  for  smaller  column  bas^s,  the  results  nay  bo  reversed. 

The  transverse  reinforcement  under  columns  also  is  not  calculated; 
nor  •'the  amounts  of  reverse  bonding  moment  bars  for  the  -min  reinforcement.  The 
student  s  hould  supply  these  computations  with  design  sketches. 

Consult  Eng.  Record,  Vol.  64,  Oct.  28  ,1911,  p.  506,  for  a  description 
of  a  Reinforced  Concrete  Candy  Factory.  Eoro  is  illustrated  a  trapezoidal  footing 
Fig.  32A  for  whose  bottom  slab  the  main  reinforcement  runs  laterally,  since  the 
column  leads  are  transmit  t  cd  to  the  slab  by  a  connecting  girder  6'6;1  wide  x 
5'0"  dee. 


COMBINED  FOOTINGS  OF  STRUCTURAL  STEEL  I  -SHAMS  Al-iD   COk 
In  proportioning  areas   for  adjacent  grillage   footings,    they  are 

frequently  found  to  overlap  and   in  such  castss   two,   three   or  even  four  areas  may  be 
combined  into   ono   footing.   In  some   of  tho  more   recent  designs  complex  foundations 
have  been  built    in  reinforced  concrete  but   in  the  majority  of  instances   recourse 
has  been  had  to  the  use   of  grillages   of  I  -beams.    In  typical   examples  r  number  of 


:;,  i  •:..' 


91 

•  columns  rest  upon  a  straight,   continuous  girder,  which  in  turn  is  supported  by 
one   or  more  layers  of  short  grillage  beams.    For  exceptionally  heavy  work  the 
continuous  I-girder  bocoro  s  a  neat   of  I-beams,  a  plate  girder  or  evon  a  truss. 
The  same  principles  of  design  apply  whether  the  type  is  reinforced  concrete  slabs, 
rolled  steel  I-beams  or  plate  girders.    In  the   following  analyses  the   cases  consider- 
ed picture  only  groups  of  I-beams   imbodc'od  i-n  concrete. 

Combined  footings   of  I^becm  grillages  are  much  used  with  the  canti- 
lever construction  and  where  lot    linos   limit  the   spread  of  one  part  of  a  foundation. 
Thore  are  nrajiy  possible  combinations  requiring   special  solutions.   The  problem  is 
much  simplified  when  only  two  tiers   of  beams  aro  used.    The   examples  presented 
below  arc  taken  in  part   from  Frcitag's  Architectural  Engineering,   Chap.    IX,   on 
Foundations. 

TWO  UNEQUAL  COLUMN   LOAlfe  SUPPORTED  UPON  A  HECTAHGULAF.  GRILLAGE 

In  Fig.   33  lot  A  and  B  be  two   column  loads   spaced  a  distance  m. 

The  lot   line   is  adjacent  to  the   lighter  column;     A<.B.    It   is  required  to  design  a 
footing  of  two   tiers   of  I-beams  whose   foundation  bed  is   rectangular,  b  x  1. 

If  tho  weight  of  grillage  P  is  neglected  and  the  allowable    foundation 
pressure  is  p,   the  croa  k  of  footing  bed  is  : 

k  =  bl  =  A  +  B/p («9) 

Let  x  =  tho  distance  from  column  A  to  the  line  of  action  of  tho 
o 

resultant  load  A+  B.  Tho  value  of  x0  is  given  by  equation  33.  In  order  that  the 
controid  of  the  rectangle  and  the  center  of  loading  mr.y  coincide: 

1  =  2  xo  *  2  fin/  A  +  B (40) 

Hence,  b  =  k/1 ' (41) 

The  upper  tier  of  beams  will  be  few  in  number,  of  length  1,  The 
group  will  have  a  total  plan  width  c.  They  are  continuous  beams  of  two  spans, 
m  and  a;  a  being  a  cantilever  span.  If  w  =  the  uniform  pressure  per  lineal  ft.  of 

footing: 

w  =  A  +  B/l  =  pb l4' 

This  is  the  intensity  of  load  par  lineal  ft.  acting  upon  tho  uppsr 


.'"'.'•  '•    --•'•'••      '•     '*;.''• 


92 

tier  of  beams  whoso  two  spans  m  and  a  are  supported  by  the  two  reactions  A  r.nd  B. 
If  d  is  tho   spacing  in  ft.   of  the  cross   beams  in   the   lower  tier,    the-  total   laid 

T7     on  one  bean  is  , 

T7  *  wd  .    .    .    .    .    .    .    .    .    .    .    .    .    ,    .    .    .    .    .    .    .    .    .    (43) 

and  the  maximum  bonding  .nomont  LI  is  by  equation  23,  M  =  V//8   (b~c).    ....      (44). 

For  simplicity  an  appropriation  is  made  by  considering   the  center 
line   of  column  A  as  the  end  of   tho   footing.    The  error   is   slight  particularly  if 
tho  span  m  is  largo  in  comparison  to   the   column  base  which  usually  is   loss  than 
2  (ft.  square,   since  tho  bearing  is  metallic.    For  the  upper  tier  tv/o  rc.x.   bonding 
moments  MI  and  !1%  will  bo  found,   one  at  the  section  -of   zero  shear  in  spai   m,   the 
other  at  column  B.    If  g  is  the  distance   of  section  IIj   from  A: 

g  =  A/w o    .    (45) 

%  =  Ag  -  wg2/2 ,   V  .    .   . (46) 

If  the  base  of  column  B  has  a  width  c,  1,1     =  wa2/  2  -  Bc/8  .........      (47) 

(~j 

;Thc  maximum  shears  in  the  upper  tior  of  beams  occur  at  tho  columns. 
A  small  distance  to  the  right  of  A  the  shear  is  the  load  A;  immediately  to  the 
right  of  column  B  it  may  be  taken  equal  to  va  while  to  tl::-  left  of  that'  column 
it  is  B  -  wa. 

Uhen  the  wall  column  carries  the  Irxgcr  load,  A>  B,  this  method 

fails  since  the  lot  lino  would  prohibit  the  projection  of  a  cantilever  span  to  the 
left  of  column  A. 

/ 

Numerical  Example.   In  Fig.  33,  let  ::  =  220  tons,  B  =  400  tons,  m  = 
12  ft«,  p  =  4  tons  per  sq.  ft.  By  equation  39,  k  =  155  sq.  ft.  By  equation  40, 

1  =  2  z  400  x  12  ^  15.5  ft.  By  qquation  41,  b  =  10  ft.  By  equation  €2,  w  =  4:r  10s= 

220  +  400 
40  tons  per  lineal  ft.  By  equation  45,  g  =  220/40  -  5.5  ft.;  by  equation  46,  Llx= 

220  x  5.5  -  40  x  .(5.5)2  =  +605  ft.  tons.  The  metal  base  of  column  B  rests  on  stool 

2 

beams;  therefore  assume  a  base  width  c  =  42  ins.;  this  value  will  give  an  excess- 
ively low  bearing  pressure  for  steel  on  steel.  By  equation  47  M£  *=  -  40  x  (3.5)2+ 

M 

400  x  5.5-    =  _  71.Q  ft,    tons.    In  this  problem  it  is  sc.n  that  ;/!]_>  Lig;  with  3 

8 
larger,    tho  cantilever  length  a  rould  increase  till    finally  LI2  ^'ould  c-xcccd  U-,_    . 


• 


' 


PC 


..    i 


93  . 

The  section  modulus  for  tier  1  Is  605  x  2000  x  12  =S08,  requiring  5  -  24"  85# 

16000 
I-beams  in  bending.  The  beans  must  be  hold  together  securely  by  separators  and 

bolts.  The  spaces  bctvoen  are  filled  with,  concrete™ 

Sh_ecr.  The  shearing  stresses  in  the  v/obs  of  the  I  -beams  of  tier  1 

should  be  investigated.  The  shear  near  A  *  220  tone;  to  the  left  of  3  =  260  tons  ; 
to  the  right  of  B  =  140  tons.  Hence  tho  greatest  shear  intensity  in  the  webs  = 

S  =  3/£  x  260  x  2000  IDS.  per  sc.  in,;  where  n  =  number  of  beams  in  tier  1,  d  = 

tndt 
depth"  of.  those  beams  in  ins.,  and  t  =  their  web  thickness  in  ins.  For  t  he  5  -  24" 

85#  I-beams  required  for  the  bending  moment  I^,  n  =  5,  d  =  24  ins.,  t  =  0.57; 
hence  S]_  =  11400  Ib.  per  sq.  in.,  a  value  which  is  conservative  and  indicates 
about  the  s  ame  degree  of  safety  as  the  16000  Ibs.  per  sc  .  in.  working  stress  em- 
ployed for  bending  stresses.  Allowing  about  2  1/2  in.  spaces  between  flanges  to 
pour  concrete,  'c  =  5  x  7  +  4  x  2.  5  =  45  ins, 

Design  of  tier  2  -  Consider  d  =  1  ft.;  by  eq.  43  \7  =  40  tons,  by 
(44)  iJL  =  40/8  (10  -  3.75)  =  31.2ft.  tons,  per  lineal  ft,  of  footing,  section      » 

modulus  =  51.2  x  2000  x  12  =  46.8;  use  12"  31.  S^  I's  at  9  1/4"  centers.  The 

16000 
maximum  shear  is  at  section  QQ  =  40  y.  5.12  =  12.5  tons  uer  lineal  ft.  of  tier  2  = 

10 
9.6  tons  per  beam  for  9  1/4"  spacing.  Henco  the  rax.  shear  intensity's  =  3/2 

9.6  x  2000  =  6850  Ib.  per  sq.  in.  of  web. 
12  x  0.35 

TWO  UKECUAL  COLUf/E   LOADS,    THE  GREATER  LOAD  AT  THE  LOT   LINE, 

H)  upou  A  TR.PSZOID.'.L  GRILLAOZ  OF  TV/O  Tizrs  OF 


x 


In  Fig.  34  use  notation  similar  to  that  of  Fig.  32.  Column  A  at  the 
lot  line  has  lord.  A}>  B.  The  distance  y.  from  the  trapozoid's  centroid  to  the  line 
of  column  A  is  found  by  ec.  33.  Neglecting  tho  w  eight  of  footing  P,  its  area  k  is 
giveniby  oq.  34.  By  static  moments  about  any  point  in  the  lot  line,  a:- 

bl2*  (a  -  b)l2  =  k  (x0  +  yj> (48) 

2        6  " 

Equation  35  and  equation  48  contain  two  unknown  quantities,  a  and 

b,  solving:Q  a  =  2k  (  2  -5(xn+y)   ) (49) 

1        1 

b  =  2k  (  3(v,,+  v)  i\  (5°) 


94 

In  footings   for  which  tho  span  m  is   large  compared  to   the  dimensions 
of  column  bases,    tho  distance  y  and  z  may  bo  neglected,  ifeking  y=z=0,m=l,' 

and  :  - 

a  =  2k/l    (2-  5xn)      ;   b  =  2k/l   (Sx^  -  1   }...,......**.    (51) 

~1  1 

The  upper  tier  of  beams  is   loaded  with  an  intensity  wj  at  edge  b; 

Cu 

w2  at  edge^.  The  load  varies  linearly  between   those   lioits.  At  any  intermediate 
section  'the  intensity  is  proportional  to  tho  width  of  the  trapezoidal  footing. 
Since  p  denotes  tho  allowable  unit    footing  pressure,  \Vj=pb;     v/2=  pa.  ........    (52) 

By  scaling  the  pressure   diagrr.m,    or   from  similar  triangles  by 

computation  we  may  got  tho   values   of  \va  and  w-Q  under  the  respective  column  centers, 
If  y  and  z  are  considered  negligible,  w-^  =  wb  and  w2  =  w,,.  Measure   tho  variable 
distance  x  from  column  B  to  the   left,  then  the   load  intensity  at  any  section  is: 
w  =  wb  +   (wa  -  wb)  x/1   ....................    (53) 

Neglect  the  restraining  cantilever  effects   in  tier  1  produced  by 
tho  soil  pressures  at  tho  dnds  y  and  z.    Consider  tho  girder  of  tier  1  .simply 
supported  on  span  m  =  1.   For  t  he  assumptions  the  reactions  are  A  and  B.   The 
bending  moment  M  at  any  section  XT    is:- 

•*  "V-» 


M  =  Bx]_  -    /  w(xi  -  x)  dx  .......  .  .........  (54) 

6 

M  maybe  evaluated  from  (54,-)  by  considering  -x^  a  c  onstant  r.nd  sub- 
stituting the  value  of  w  from  (53);  but  in  what  follows  X]_  is  a  variable;  see 

equations  (55)  and  (56). 

/ 
M  =  Bxl  -  /  (wb  +  (wa  -  Wb)x/l)(xi-x)dx. 

Expanding  and  integrating: 

M  «  Bxi  -IwwKlX  -  (wb~  (w0  -  v/b(J)  xx  )  x2/2  -  (wa-wb)  x3/3  1 


Substituting  the  limits,  wo  get  tho  bending  moment  at  any  section: 
M  =  Bx 


The  m?.ximum  bonding  moment  M0  occurs  at  section  xx  =  g,  whore  tho 

.-hoar  is   zero.   Tho    first  derivative   of  M  v/ith  respect  to  x  is: 

=  s  =  B  -  v/b*i  -   (wa-  wb)   xi2/  21 


95 


v/hcn  the    shear  s   =  0,  x     =  g,   henCe: 

0  =  B  -  wbg  *•  (wa-v.'t>)g2      ;   solving  for  g, 


g  =  -  wbl     -i-  *f~w~izT<£  •  +  2B1 

_  ...............    (57) 


MO  =/B^-A^bg2J  -  (wa  -  wb)   g3/  6  1   ...............    (58) 

c*/L 

iracTical  problems  it   is   often  b  ost  .to  calculate  the  value  of 

each  quantity  in  turn.  By  introducing  the  numerical  r. suits   in  succession  into 
the  subsequent  equations  the  complexity  of  algebraic   forms  like    (57)   is  eliminated 

The  beams  of  tier  1,   v/hon  uniform  in  section  throughout  the  span, 
are  designed  for  the    shear  s  =  A  and  b  ending  moment  I«10.    For  very  heavy  footings, 
for  economy,  the  beams  of  tier  1  may  be  plate  girders  whose  webs  and  stiffeners 
vary  in  dimensions  to   suit   the  value  s  from  eq.    (56)   and  whose  flanges  are  pro- 
portioned  to  withstand  the   v£rying  bending  moment  M  of  oq.    (55).    For  an  analysis 
equivalent  to  t he  above,    see  Frcitag,  Architectural  Engineering,   1909,  p.    331. 

The   lengths  of  the  beams  in  the   lower  or  second  tier  vary  from  b  to 
a.   The  total  load  on  a  b  earn  at  a  would  be  w2d,  where  d  is  f  o  spacing  of  beams; 
similarly  at  bx  the-  total  load  would  be  wxd.   For  an  intermediate  beam  at  section 
x  the   load  would b e  wd.    Separate  calculations  have  been  illustrated   fully  in  two 
earlier   examples.  As  already  explained  for  the   trapesoid  of  reinforced  concrete, 
Fig.    32,  here  also,   the  method  fails  when  column  load  B  is  equal  to   or  less  than 
one  half  of  load  A.   For -B  =  A/2,  vq.  ' 

'..' 

'  '"  ,  .      consult  Frog's  Architectural  EnSineoring,  p.  S*»i   International 
correspondence  School,  Structural  EnSinoering  Course,  Heavy  Foundations,  p.  24. 

V 

Sec  also  reference  No.  9  at  the  end  o'f  this  cjjaptoi 

In  Fig.  35  consider  three  columns,  loads  PI.  P2,  *g>  ' 

r  1  Neglecting  the  footing  weight: 
spaced,  supported  on  a  rectangular  base  b  . 

pbl  =  Pi   +  P2  +  PS 

Hore  p  -  allege  pressure  en  the  soil.  For  uni.™  distribution,   the  center  of 


96 
gravity  of  the   loads  P  must  coir.cide  with  the  centroid  of  the  rectangle,   or 

1/2   =  P1:ni   +  P2(rai-H7i2J    +  P3(mi-wi2-«r-3)    ............        ....    (60) 


pl  +  ?2  +  ^3 
To  satisfy  these  relations  the  girders  must  be  stiff  and  suffer 

little  deflection.  The  dimensions  m  and  the  loads  P  must  be  arranged  to  fit.  If 
these  conditions  cannot  be  fulfilled  the  pressure  p  vd.ll  not  be  uniform  unless 
the  breadth  b  israade  variable.  A  changing  value  of  b  throughout  the  footing 
length  introduces  further  complexity  and  indetermi  nation.  For  cases  v.hich  do  not 
ueet  the  requirements  of  (59)  and  (60)  easily,  the  continuous  footing  type  should 
be  discarded.  Instead  separate  footings,  pile  clusters,  or  caissons  may  be 

selected. 

To  design  the  beams   of  tier  1  it  is  necessary  t  o  find  the  max. 
shears  and  bending  moments.    The  pressure   against  the  beams   from  below  is  pb.   From 

above,  under  Pl  it<is  PI/XI  =  p,  ,  under  P^  it  is  p2  =  ?2/x2;  and  P3  =  P3/X3"  The 
i-.iax.  bending  moments  are  111,  1/12,  143,  etc.  at  distcnces  Ij,  l2>  ls»  etc-  from  ^e 
left  end  of  footing,  at  sections  for  which  t  he  shc-ars  are  zero.  For  the  notation 


shows:-  pbli  =  PlU]_-yi)»    fr0™  which  1     =  p1y1 (61) 


pb!2  =  PX,   or  12  =  Pi/pb 

=  PI  *  pat  is-yi-x-yg).  or  1s  =  pi-P2(yi  >xi  *yz)       ....    (63) 


Similar  equations  maybe  established  f  or  t  he  remaining  sections  of 
zero  shear  at   distances  14  and  lg.    The  max.    bending  moments  Ml,  M2,   etc.  result 
by  toeing  in  each  case  the  algebraic  sum  of  moments  of  pressures  to   the  left   of 
the  section  about  the  section. 

MI  =  pbli2/  2  -  PiUj-yil?        -    •    • (64) 

fy 

112  =  pbl22/2  -  P-.M^-tr. -XT  1     '• t65) 


.  ?1    {1     y     Xl    )    -  P2   (l5-yi-xry2)^     . '.    166) 

3       -2  '—, : 


The  expressions   for  M4  and  :.I5  are  easily  written.      If  z^  *2  and  x3  are  relatively 
small  and  their  effects  on  MI,  M3  and  Ilg  are  neglected,  the  max.    shears  are  th( 


97 

following:      s^   =  pbmi  and  S2   *   SI-PI %    ....    (67) 

S3  =  pb(mi+ra2)   -  P},s4  =  s3-  P2 (68) 

She   values  for s 5  and  35  are  easily  written.    If  the  pressures  pi, 
P2 '  P3  are  considered,    the   shears     are  somewhat  reduced,    so  that  the   values 
(67),    (68)   etc.   give  results  on  the  safe  side. 

If  the  girder  of  tier  1  consists   of  a  neat  of  I-beams  the  design  is 
decided  by  the  greatest  M  and  sj   Aquations   (64)   to    (68).   If  a  plate  girder  is  used 
the  webs  and  flangos  maybe  made  to  vary  inr/eights   to  suit   the  different  paxima. 
The  cross   beams  under  the  belumn  bases  and  the  transverse  bea.ns   of 
tier  2  are  designed  in  the  usual  manner,   see   eq.    (23). 

PARTIAL  APPLICATIOn  OF  THE  PRINCIPLES  OF  TItEEE  MO:fflKTS. 
Strictly  speaking  this  theorem  is   inapplicable,  particularJ.5'  for 
extended  slabs  of  large   length  1  supporting  four  or  more  columns.  Assuming  a 
uniform  soil  pressure  p,    the  column  shears  s, ,   s2,  etc.     and  the  column  moments 
M-p  MS,  M5  etc.  result  by  computation.   For  unrestrained  elastic  action  of  the 
bending  moments  throughout   the  spans  mi,  m2  etc.    there  must  be  appreciable  de- 
flection which  would  lessen  the  pressure   intensity  p  near  the  span  centers  and 
increase   it  under  the  columns;   Bhus  destroying  a  prime  assumption.    But   furthermore 
for  equilibrium  of  vertical  forces  s-^sg  =  Pj,   s2  +  s3  *  P2,   etc.    Such  equalities 
can  only  obtain  after   repeated  trials.    It  would  be  a  practical  difficulty  to  pro- 
portiom  the  span  lengths  m  and  to  adjust  the   column  leads  P  to  meet  the  above 
conditions  at   the  same  time  that  a  uniform  soil  pressure  p  was  maintained  by  a 
coincidence  of  the  centers  of  loading  and  footing  areas.    It  would  require   limi- 
tations to  the  architect's   freedom  in  planning  floor  panels  and  column  positions 
that  might  be  completely  objectionable.   Hovover,   the  preceding  analysis,  equation 
59   to  68  in  great  part  is   open  to  the  same  objections.   As  an  instructive  analytic 
problem  the  theorem  of  three  moments  will  be  applied  to  the   case   of  Fig.   35,  three 

columns  and  four  spans. 

For   simplicity  assume   that  the  column  bases  xi,  x2,x3     are   : 
relatively  to  mlf  m2,  m3,  n*,  so   that  the  loads    from  -above  are  applied  essentially 


! 


98 

at  points.   Tho  two  end  moments  M,   and  Mg  are  known  because  the   spans  raj  and,m4 
ere  cantilevers:-     M]_  =  pbm].2/2;  M5  =  pbm42/2  .....    ...    .......    (69) 

Applying  the   theorem  of  three  moments  to  spans  m2  and  m^:- 

Mlm2   +  §M3(m2+m3)    +151713   =  -  pb/4   (m23+  m33j;--    ..........    .    (70) 

Eq.    70  contains  only  one  unknown,   M^;   hence, 

+  M].m2 


~   - 


(71) 


2(m2  -17113) 
For  the  end  spans:-  si   -  pbm]_;    85  =  pbm4  ..................    (72) 

In  span  m2,   taking  external  moments  rbout  column  P2:- 

s2m2   -»  pbm22/2  -  Mi+Mg  =0;  hence   sg  '=  pbm2/2  •*•  Mj-IJg   .......    ;    .    .    (73) 

m2 
By  taking  moments,    similarly,  about  Pj,   PS  and  P2, 

33   =  pbm2/2   -  Mi-M3      .........    .    ......    .......    (74) 

^  m2 

A- 

+  1,1^-1.15.    .    .    .    .................  '.    .    (75) 

mg 


=  pbms/2   -  J%- 
'ra3 


The  maximum  moment  M2  in  span  m2  is  found  at  section  12  v/hore  the  shear  is  zero. 
Lot  g]_  =  12-m:   S2  =pbg!  =  0;  g]=  s2/pb.  ...  .............  (77) 

M2  -  -Ml  +  S2gl  -  pbg^2,  ...........  ............  (78) 

Similarly  M4  =  -  MS  +  s4g2  -  pbg22/2  ....................    (79) 

The  analysis,   equations  69  to   79,   depends  upon  the  condition  that  s-^+sg  :=  PI» 

^Z*B&  ~  P2;   S5  *  S6  =  P3'   and  upon  the   satisf&ction  of  equations  59  and  60. 

Special  Case.    Suppose   the  design  is    symmetrical  about  the  line   of 
column  P2.   Then  the  center  of  loading  and  the  ccntroid  of  footing  are  under  that 
column;-  ml   +  m2  =  1/2;   PI  =  P3,  rr^  =  m4;  m2  =  'm^ 
From   (69  1,   HI  -  Mg  =  pbmi.2/2   .......................    (8I 

From  (71),   M3   =  -  pb/8   (m22   +  Smj2)    .....    .    .............. 

From   (72),   si   =  S6  =  pbm;   .........    ................ 

From  f73),   s2  =  s5  =  pb/8m2(3n?2£   +  2ml2)    ....    .............    ^8 

From   (74),    S3  =  s4  =Pb/8m2(5n22-  2m]2)    ......    ............ 


99       f 

From   (77),   g     =  m2-g2  =  5m^2   4-  2m^_     .......    4 .    (85) 

8mg 
From  (78),  M2  =  %  =  pb/lZBa&Z  (9rn24  -  S^SceS+tal^)    ..........    (86) 

Further          si+s2   =  PI  =  Pg   £  pb/9m2(3m22  +  8mim2   +  2mi2) (87) 

S3   +  34  =  P2  =  pb/4m2(5m22   -  Sm^) (88) 

numerical  Example.      Suppose  in  Fig.    35,  p  =  3  tons  per   sq.    ft., 
Pi  =  PS  =  40O  tons,  P2  =  250  tons  and  that   the  lot  dimension  1  =  40   ft.    Fron 
(59)   bl  =  1050/3  =  350  sq.ft.,  b  =  350/40  =  8.75   ft.    For  symmetry  about  P2s 
2(m1   +  m2)   =40   ft.      Hence,  m>    -  20   -  m2   .    ...    .    .    .    .    ....    .    .    ...    (89) 

From  (87)  3m22  +  8m]m2   +  2mi2       =  8Pi/pb  ~  8  x  400     =  122   ft (90) 

ffig ' 3  x  8.75 

From   (88),    5m22    -  2ai2      =  4P2/pb  =  4  X  250        =  38.1   ft. (91^ 

m2  S  x  8.75 

Either   (90)   or   (91)   combined  independently  with   (89)  v/ill  give   the  values  of  m 

and  m2.    Considering   (89)  and    (91) :t  fim22  -  2(20-m2)2  =  38.1m2 

Solving,  ra2  =  +10.8   ft.    or  -  24.8   ft.;    the  rational   value   is  m2  =  10.8  ft.J 

hence  m]_  =  9.2   ft.   Equations  82  to  84  give  the  max.    shears;   80  and  81  and  36 

the  :jax.    bending  moments.  If  the   column  loads  are  distributed  upon  tier  1  over 

base  widths  x^  and  x2,    the  moments  and   shears  at  columns  v/ill  be  reduced. 

ECCEl.'TRIC  STEKL  BEArl  GRILLAGE  FOUNDATIONS , 
NA?IV3  SONS   HlLL,    SAL'  FRANCISCO 

Fig.    35A  shova  a  line   of  four   structural  steel  wall  columns,  Nos. 

• 

3,4,5,6,    supported  upon  a  layer  of  5  15"  42#I-beavns.   The  beam  layer   in  turn  is 
imbedded  in  and  upon  a  concrete   base  3'9"  \7ide  by  50 '4"   long.  There   is  a  bed  of 
12"   of  concrete  under  the  beams.    The  steel  columns  have  their  axes  8  1/2  inches 
from  the   long  center  line   of  the    footing,   thus  producing  a  tilting  moment  which 
would  give   increased  pressure  at   the   lot   line.   To  offset  this  eccentricity  two 
15"   65irl-beams  extend   from  e^jchwall  column  to  the   interior   footings  Nos.  40,41, 
42,43.    The  tilting  moment   therefore  t  ends   to   lift  the   interior  colu.nns,   relieving 
weight  upon  their  bases  and_ producing  central  pressure   on  the  wall  grillage.   The 
foundation  rests  on  dry  sand;    the  design  pressure  being  about  3.5  tons  per  sq.ft. 
The   total   load  on  the    four  wall c olumns   is   1,140,000   Ibs .  The   largest  column, 
No.    6,   carries  313,000  Ibs.  which  for  an   eccentricity  of  8  1/2  inches  gives  a 


T  • 


moment  of  2,650,000  In.  Ib.  upon  the  wall  grillage.  This  moment  is  resisted  by 
the  two  15"  65#I-bea7is  end  produces  an  uplift  at  column  43  of  about  11,000  Ibs. 
The  total  load  on  the  wall  footing  is  increased  by  the  same  amounts 

Co  nsult  Engineering  Record,  Vol.  64,  Oct. 28, 1911,  £.  508,  for 
foundation  girders  in  the  United  Fire  CompaniesBldg. ,  Kow  York,  where  the  same 
principle  was  used  as  in  the  iiative  Sons  Kail,  but  for  much  heavier  loads, 
necessitating  the  use  of  plate  girder  grillage  and  balrnce  beams. 

CANTILEVER  SPREAD  FOOTINGS  OF  RIII^TOBCLD  CONCRETE 

Fig.  35B  illustrates  a  cantilever  footing  designed  in  reinforced 
concrete  for  the  proposed  Regents  Hotel,  San  Francisco,  using  the  principles  just 
described  in  Fig.  35A.  To  bring  the  center  of  the  structural  steol  column  No.  59 
v/ithin  8  1/2"  of  the  lot  line  required  an  eccentric  cast  iron  base  similar  to 
Fig.  27B.  The  total  load  on  column  59  is  442,000  IDS.,  eccentric  1.8  ft.  from  the 
center  of  the  rectangular  footing,  12  ft.  long  by  5  ft.  wide.  Column  48,  inhich 
otherwise  would  rest  upor  a  footing  similar  to  Fi&.  27A,  acts  as  an  anchorage. 
The  load  on  column  48  is  630,000  Ibs.  The  relief,  45,000  Ibs.  through  cantilever 
action  reduces  the  effective  load  to  585,000  Ibs.  Additional  load  thus  is  trans- 
ferred to  the  footing  under  col  umn  59,  v/hich  receives  a  total  of  487,000  Ibs. 
The  tilting  moment  at  footing  59  is  45,000  x  17.5  x  12  =  9,500,000  in.  -Ibs.  The 
concrete  beam  36"  wide  by  40"  deep,  Ag  -  14.5  sq.  in.,  is  in  cantilever  bending, 
the  moment  decreasing  toward  column  48.  This  building  rests  on  dry  sand.  The 
footings  v/ere  designed  for  a  pressure  of  about  4  tons  per  sq,  ft.  The  student 
should  check  the  design  to  determine  the  stresses  in  concrete  and.  steel  for  the 
two  footings  and  their  connecting  beam.  Since  the  concrete  of  the  foundation 
rests  directly  on  the  sand  the  weight  of  the  two  footings  and  cantilever  beam 
is  not  included  in  the  a'^ove  bending  calculations.  In  this  design  rather  high 
working  stresses  wero  used. 

For  discussion  and  illustration  of  similar  concrete  footings,  see 
1.  Concrete  Building  with  Composite  Column  Foundations,  Eng.  Eec.  Vol.  65,  Mar. 
23,1912,  p.  324;  2,  Spread  Footings  for  Large  Concrete  Factory,  Eng.  Record, 


101 
Vol.    65,   June  22,    1912,  p.    682, 

ADDITION!,  ICFSBSIjCES,      SPREAD  FOOTIflSS.  ...,*' 


1=  Architects  and  Builders  Pocket  Book;   F.JJ.Kidder,   Chap.    II,   Foundations 
and  Spread  Footings;   Chap.  .Ill,  Hasonry    Walls  and  Footings 

2,  International  Correspondence  School,   Structural  Engineering  Course, 
The  Statics   of  Llasonry,  Parts   1,   2,   3;   Heavy  Foundations. 

3.  Foundations  for  the  Phelan  Building,    San  Frr.no isco;  Eng.  Record, 
Vol.    57,   p.    366,   March  28,1908. 

4.    Foundations  for   the  Call  Building,   San  Francisco;  Architectural 
Engineering,    Freitag,  2d,   efl. ,    1909,   p.   339;   also  ling.  Record,  Apr. 9, 1898. 

5.   The  Humboldt  Savings  Bank,   San  Francisco;   Eng.   Roc.   Vol.    58,  Uov.21, 
1908,   p.    581. 

s 

60  Development  of  Building  Foundations;  F.  77.  Skinner;  Eng.  Eecord, 
Vol.  57,  Apr.  4,1908,  p.  412, 

7.  Stress?s  in  Steel  Fovndction  Footing  of  I -beams  and  Concrete,  Using 
the  Theory  of  Continuous  Beams;  Eng.  Record,  Vol.  39,  1899, pp.  335,  354,  383.,  407. 

8.  C,T.Purdy,  Steel  Foundations;  Footings  of  I-beams  ar.d  Concrete; 
Approximate  Methods;  Eng.  Bev/s,  Vol.  26,  1891.  pp.  116,  122,  265,  312,  415, 

9.  Analysis  of  the  Continuous  Three-Column  Foundation,  by  C..'-. Ellis, 
.Ing.  News-Record,  Vol.  85,  Oct. 7, 1920,  p.  680. 

PROBLEMS 

1.  A  retaining  wall   of  concrete,   back   face  vertical,    front   face  battered 
1  E  to  3  V,    is     2  ft.    thick  at  top;   the   earth  slope  behind  wall  is  plane,   sur- 
charged on  angle   of  10°;   $  the  angle  of  repose  =  32*,   the  weight  of  earth  is 
120  Ib.  per  c-  .ft.  Upon  a  horizontal  joint  32  f  .    from  the  top  find  the  center  of 
-pressure,   the  range  of  pressure   intensity  and  the  max.  and  rain  values,   the 
stability  agcinst  sliding.   Use  Pisnkine's   formulas  for  earth  thrust. 

2-   A  cement  jointed  brick  wall  thoroughly  waterproofed   is  18  in.    thick. 
If  it  retains  v/ater  'whose   free  surface   is  coincident  with  the  wall   top,   at  what 
depth  is  the  center  of  prc-s'ure  at  the   :iiddle  third  of  a  horizontal  joint?  For 
-his   joint  what   is   the   -.Tax.    intensity  of  pressure? 

3.  A  sub-be sement  v/all  of  reinforced  concrete   is  12  ft.    6  in.  high  between 
loors  A  and  B;   the  upper  floor  A   is  7  ft.    be^r  the  horizontal  ground  surface, 
he  wall  t  ekes   only  lateral  pressure   from  ths  retained  wet  earth.   Design  a  ver- 
%  ical  strip  of  •'all  12"  wide,   using  specifications  of  the  San  Francisco  Ordinance 
uppose  the  vail  panel  rests  between  two  columns   14   ft.    6  in.  apart.    Compute  the 
Ocds   corning  upon  reinforced  concrete   bea.is  running  horizontally  between  columns 
•ic    at  the  levels  A  and  B  if  the  biams   support  tl'.e  bulging  pressures   from  the 
T.ll=    Design  the  beams. 

4.  A  cylinder  shell  of  concrete  maso  nry  has   its  inside  surfece  a  right 
ylinder  of  eicmeter  2  ft.    5   in.   Tho   shell  is  9    in.   thick  at  the   top,  24   in.   at 
:;e   bottom  and  of  height   85  ft.   From  dead  weight  what   is  the  presiure  at  tl:G  bottom 


. 


102. 

joint  assuming  the  load  uniformly  distributed?  Considering  the  trapezoidcl 
meridian  section  es  bringing  the  weight  ecdentric  on  the  circular  basal  ring,  what 
is  the  minium::!  and  v.'he.t  the  njaximum  intensity  ^for  outer  ?nd  inner  points  of  the 
base  section?  For  a  wind  blowing  with  pressure  20  Ib.  per  sc.  ft.  of  vertical 
projection,  v/hat  ,nin.  and  max.  pressures  are  exerted  whin  combining  dead  with 
wind  forces? 

5.  For  the  Great  -Falls,  IJontcna,  chimney  described  in  Eng.  Record,  Nov. 
28,1908,  compute  the  stresses  and  investigate  stability  of  a  joint  80  ft.  from 
the  base,  when  the  wind  is  blowing  v/ith  a  horizontal  pressure  of  20  Ib.  per  sq. 
ft.  'of  vertical  projection. 

6.  Design  a  concrete  c.butnent  to  withstand  £n  srcli  thrust  of  130,000 
Ib.  per  lineal  ft.  of  bridge  width,  if  the  thrust  acts  at  e.  point  in  the  fsce  of 
the  kbutment  20  ft.  below  tha  roadway  and  at  an  angle  of  28"  to  t  ha  horizontal. 
Determine  the  necessary  length  of  s.  joint  40  ft.  below  the  roadway  r  osting  upon 
hardpan. 

7.  If  a  soil  may  carry  2  1/2  tons  per  sc.  ft.  design  a  timber  footing 
of  yellow  pine  to  support  a  column  load  of  300,000  Ibs..,  allowable  timber'  fiber 
stress  1000  Ibs.  per  sq.  in.,  compression  across  grain  200  Ib.  per  sq.  in. 

8.  For  the  timber  grillage  of  prob.  7  substitute  a  solid  c  oncrete  footing 
with  stepped  offsets;  allowable  cross  breaking  strength  of  concrete  30  Ib.  per 

sq.  in.;  compression  500  Ib,  persq.  in. 

9.  The  load,  ona  cast  iron  colusm  base  is  300,000  Ib.  neglecting  the 
footing  weight,  design  the  cast  iron  b;  se,  a  stepped  brick  pier  laid  in  cement 
mortar  with  a  concrete  bed  end  bluestono  pap,  the  safe  bearing  value  of  the  soil 
being  4  tons  per  sq.  ft.;  of  the  brickwork  2000  Ib.  per  sc.  in.,  of  concrete  400 

and  of  the  bluestone  cap  §00  Ib.  per  so.  in. 


10.  Design  a  steel  grillage,    like  Fig.  26,   of  square  bed,    total  load  on 
foundation  bed  500   tons,    safe  soil  pressure  =  3  3/4  tons  per  so.    ft.,  pressure 
on  cast   iron  base  =  375  Ib.   per  sq.   in.,   allowable  shear   in  beam  webs  =  10,000 
Ib.    ,    fiber  stress  =  18,000  Ib.  per  sq,    in. 

11.  Design  a  square  reinforced  footing,    like  Fig.    30,    total  load  500,000 
Ibs.,   soil  pressure  4  tons,  per  sq.    ft,,   bearing  cast   iron  column  base    =r  350  Ib  . 
per  sq.    in,,   allowable  concrete  shear  =^-75  Ib.  ,   compression  =  500  Ibs,,    steal 
bars  in  tension  =  16,000  Ibs.,  bond  =  125  Ibs.    for  deforce!  bars,   all  in  Ibs.   per 
sq.    in* 

12.  Design  a  rectangular     rolled   steel  bea-.n  g  rillagt  ,    like  Fig.    33,   to 
support   the  loads   of  prob.    13  upon  a  rectangular  footing  bed,   using  stress 
specifications   of  probs.    10  and  11. 

13.  Design  a  trapezoidel   footing  of  reinforced  concrete,    like  Fig.    32, 
columns   spaced  15   ft,,   loads  respectively  315  and  425  tons,   specifications 
similar  to  problem  11. 

14.  Design  a  trapezoidal  steelbec-m  grillage,    like  Fig.   34,   to  repl£.co   tke 
reinforced  concrete   slab  of  piob.    13, 

15.  Design  a  rectangular  I-beam  and  concrete  grillage   like  Fig.   35,    to 
surport   four  columns,   PI   =  180,   P2  =  210,   PS  =  230,   ?4  =  250   tons,  m2  =    12   ft°  » 
mj  =  14   ft.,  m4  =  16  ft.  ,p  =  3  1/4   tons  per   sq  .    ft.      Determine  1,  b,  ml  end  m5. 
Assign  the  necessary  specifications   for  unit   stresses. 


0.1 


103. 


16.  Design  a  footing  like  Fig.   32A  to  replace  that   of  prob.    15. 

17.  Design  the  footing  of  prob.    12  so  'that  the  beams   in  tier  2  of  Fig. 
'33  rtin  parallel   to    the  long  side   of  the  rectangular  bed,  replacing  tier  1  by  two 

lines  of  short   lateral  beams ,    one   sot  under  oech  column. 

18.  A  wall c olumn  center   line   is   1  ft.    3  in.    from  the   lot   line.    The 
column  carries  378,000  Its.  *   the   interior  adjacent  column  65,000  Ibs.    the   column 
spacing  is  20    ft.   4  1/2  ins.   Design  for  thesfc  two  columns  a  balanced  footing 
similar   to  Fig.35A. 

19.  Bedesign  prob.    18   in  reinforced  concrete,    see   Fig.   36B. 

20.    In  an  automobile  garage  the   center  line  of  wall  column  No.   5  is 

I  ft.   3  1/2  ins.    from  the   lot  line;    spacing  of  columns  Hos.   5  and  6   is  27  ft. 

II  in.,     ?5  =  477,000  Ibs.,   PS  =  619,000  Ibs.,  allowable  bed  pressure  = 

4  tons  per  sq.    ft.  Assume  weight  of  a   footing.   Design  a  reinforced  concrete 
spread  footing  of  rectangular  plan,   using  principle  of  Prob.    17.   The   footing 
will  be  a  huge  Tee  gir,£er,    stem  30  in.   wide  x  48  in.   deep,   Tee  4   ft.  4   in.  wide 
by  24   in.    thicl-c;   total  depth  of  girder  72  ins.    See   illustrations,   Eng.   Rec. 
Vol.    65,   p.   324. 


r.. 


104 

CHAPTER  5 
SHEET  PILING 

This  tern  is  applied  to  plan&s  of  wood,  metal,  or  reinforced  concrete 
i 

driven  vertical ly'  to  form  a  permanent  cut-off  v/all  or  bulkhead;  more  frequently 

to  produce  a  .temporary  onolostzro  for  an  area  int.-  which  it  is  rr  coseary  to  oxcavato 

• 
for  foundation  purposes.  Wooden  shoot  piling  may  bo  light,  consisting  of  thin 

boards;  or  heavy,  composed  of  stout  sticks,  solid  or  built  up  of  pieces  of 
different  sizes.  LJetal  sheet  piling  is  constructed  of  rolled  shapes  so  designed 
that  they  interlock.  There  are  numerous  schemes,  ilany  of  the  forms  are  patented. 
Concrete  piling  is  built  like  huge  tongue  and  grooved  boards.  Both  heavy  ?.nd  light 
sheet  piling  often  form  integral  parts  of  cofferdam  c onstruction. 

LIGHT  Y/OODEK'  SHEET  PILING 

The  sheet  piling  used  for  purposes  of  making  excavations  for  building 
foundations  need  seldom  be  heavier  than  3  or  4  inch  plank  and  frequently  2  or  3 
inch  thickness  will  be  sufficient.  If  the  surface  of  the  ground  outside  the  Units 

of  the  excavation  must  r  err  in  undisturbed.,  the  sheet  planks  8  to  12  ft.  in  length 
fs 

nust  be  put  in  position  edge  to  edge  around  the  outside  line  of  the  excavation 
at  the  very  outset  and  driven,  as  far  as  feasible,  usually  with  mauls  or  sledges. 
A  light  pile  driver  outfit  is  so.-;etimos  used.  If  this  condition  is  not  essential 
an  open  excavation  rnay  be  :.irde  until  the  disturbance  of  the  surrounding  ..iaterial 
reaches  its  permissible  li.nits,  necessitating  then  the  introduction  of  the  first 
tier  or  group  of  sheet  planks  in  the  manner  just  described,  but  at  some  distance 
jelow  the  ground  surface.  The  excavrtion  is  then  made  within  the  sheet  piling  as 
far  as  it  can  b  e  carrie  c"  without  removing  the  supporting  material  at  the  feet  of 
the  planks,  or  causing  the  upper  portions  to  get  out  of  proper  alignment.  Hori- 
20ntal  waling  pieces  of  proper  dimensions  varying  from  a  single  plank  of  3"  x  t 
:o  a  scantling  of  even  10"  x  12"  are  introduced  as  low  down  rs  will  give  the  proper 
support  to  the  upper  end  of  the  sheeting  after  it  is  fully  driven. 

The  excav-tion  is  thus  carried  down  as  far  as  possible  without  endagger- 
ing  the  support  of  'the  lov;er  end  of  the  sheeting  or  until  the  latter  requires 


A-  r 

•    -       : 


105 

another  horizontal  waling  piece,  in  order  to  prevent  it  fro;n  being  thrust  out  of 
position  by  the  retr.ined  material.  Another  waling  piece  is  then  introduced  and 
secured  in  position  by  proper  struts  or  braces,  after  which  the  excavation  proceeds 
as  be'fore,  with  the  introduction  of   'Other  waling  pieces  f.s  recuired  and  in  the 
manner  described,  .after  the  introduction  of  the  waling  pieces,  the  sheeting  is 
again  driven  as  fnr  as  possible,  or  until  the  upper  ends  of  the  plank  are  drawn 
down  flush  with  She  original  surface,  or  until  further  driving  would  destroy  the 
upper  end  of  the  planks  by  brooming. 

When  the  last  waling  piece  put  in  position  is  as  near  1 3)e  lower  end  of 
the  sheet  planks  as  the  excavation  cr.n  be  carried,  a  new  set  of  sheet  piles  nust 
be  started  and  driven  inside  the  first  set  and  in  precisely  the  same  nrnner.  The 
excavation  is  then  to  be  continued,  or  other  v/r.ling  pieces  introduced  successively 
until  the  excavation  is  carried  frown  to  the  desired  depth.  Fig.  36  for  wide  exca- 
vations, indicates  with  sufficient  clearness  the  general  arrangement  of  sheeting, 
waling  pieces  and  braces,  as  well  as  the  :.rn;:er  of  working  by  this  method.  The 
lower  ends  of  the  sheet  piles  should  bo  bevoled  as  shown,  so  as  to  close  tight 
against  each  other w hen  driven.  For  nrrrow  sewer  trenches  no  brace  piles  B  are 
necessary;  the  struts  I  are  placed  horizontal  .jr;  through  then,  the  two  walls  of 
the  excavation  press  against  erch  other  and  -che  whole  problem  of  bracing  is  much 
simplified.  See  the  Irtsral  braces  in  Fi^.  38. 

Excavations  cm  be  carried  down  to  d  epths  of  30  ft.  or  more  by  this 
method  with  sheeting  not  n:re  thru  3  to  4  in.  thick  if  but  little  water  be  en- 
countered. In  such  c  r.sos  is  it  .essential  to  the  safety  of  the  work  that  the 
bracing,  including  the  supports  at  the  feet  of  it,  should  be  designs d  and  pieced 
in  position  with  great  thoroughness  rnd  care.  Sheet  piling  carried  successfully 
to  a  depth  of  about  53  ft.  has  been  completely  wrecked  by  the  waters  of  a  heavy 
rainstorm  and  the  leakage  of  adjacent  wrter  mains  saturating  rnrterial  back  of  the 
sheet  Blinking  so  as  to  greatly  increase  the  pressure  which  the  bracing  hr.d  to 
carry.  The  possible  saturation  of  the  ;.r.terial  retained  by  the  sheet  planking  is 
therefore  one  of  the  exigencies  which  aus x.  always  be  considered  in  work  of  this 


106 
character,  and  be  carefully  guarded  against  as  far  as  practicable. 

The  pressure  which  the  bracing  will  have  'to  carry  in  any  given  cr.se  can- 
not be  determined  v/ith  any  great  degree  of  precision,  but  the  theory  of  earth 
pressure  affords  a  means  by  which  at  least  the  approxii'-ate  loads  on  the  brrces 
may  be  computed.  The  earth  pressure  P  in  Ibs.  per  lineal  ft.  Pig.  36,  which  may  r.ct 
upon  any  waling  piece  A,  -will  be  found  with  sufficient  accuracy  by  tricing  the 
intensity  p  due  to  a  depth  J/2  (xx+xg)  below  the  surface,  as  acting  uniformly  on 
that  portion  of  t  he  vertical  face  of  the  sheeting  found  between  the  two  horizontal 
planes  Q  and  Q1  taken  /nidwr.y  fcetWQcm  each  pair  of  waling  pieces.  This  intensity 
of  earth  pressure  p  is  to  be  found  by  the  Rr.nkine  formula  :- 

p  =  w/2  (KI  +  x2)  1  -  sin  j  ............  .  .  .  .  .  (1  ) 

1  +  s  in  0 
in  which  p  is  the  pressure  in  Ibs.  per  sc;.  ft.,  w  the  weight  per  cu.  ft.  of 

earth,  1/2  (x]_  +  xg)  the  average  depth  of  earth  on  the  waling  piece  and  tf  is  the 
angle  of  repose  of  the  earth  behind-  the  sheeting.  If  the  material  is  dry,  the 
angle  of  repose  may  b  e  t  aken  at  33°42',  corresponding  to  a  slope  of  1  1/2  hori- 
zontal to  1  vertical-.  If  on  the  other  hand,  the  material  b  ec  ones  either  partially 

or  completely  saturated  with  vr.ter,  the  rngle  of  repose  may  be  arc.  11  and  the 

.     . 
weight  per  cu.ft.  relatively  large.  The  formula  sha.  s  that  both  of  these  influences 


large  l^r  increase  the  pressure  ag:  inst  the  braces.  JJnless  the  latter  are  de- 
signed with  a,  view  to  this  contingency,  the  work  may  unexpectedly  and  completely 
be-  destroyed  by  access  of  water  to  the  material  retained  by  the  sheeting  from 
.storms,  leakage  of  adjacent  wrter  pipes  or  other  sources.  For  the  notation  given  1 
the  pressure  per  liner  1  ft.  of  hsrizontal  waling  sticlc  is,  P  =  p(xg-X]_).  ,  .  .(2) 

If  the  distance  between  braces  is  b,  the  ;.r.x.  shear  s  and  bending  moirent 
« 
H  may  be  readily  calculated.  For  deep  trenches  and  bold  design  tho  safety  of  the 

timbers  agrinst  longitudinal  shear  and  crushing  across  tr.e  grain  should  be 
particularly  investigated- 

In  the  determination  of  the  bending  strains  upon  any  waling  sticlc  or  of 
the  load  T  whiclv  any  brace  may  carry,  both  the  vrlues  of  the  angle  of  repose  rnd 
the  weight  per  cu.ft.  of  t?.:o  a  tex  ial  .::ust  be  assigned  with  some  judgment.  Dry 


107 

v  material  may  not  weigh  more  than  90  Ib.  per  cu.ft.,  whereas  wet  earth  may  reobh 
a  weight  of  120  Ib.  per  cuwft.  or  possibly  more.  Similarly  the  angle  of  repts  e 
maybe  reduced  fro.::  33°42'  to  possibly  20"  or  less. 

The  pressure^'P  against  the  waling  piece  which  will  be  carried  by  a  single 
brace,  T,  will   be  distributed  over  an  area  limited  by  the  two  horizontal  planes 
Q  and.  Q1,  rlrer.dy  described  and  by  the  midway  points  to  each  of  the   adjr.cent 
braces  spaced  a  distcnce  b.    Let  thr.t  area  be  represented  by  A  =   (xg   -  x   )b,  and 
let  the  angle  -which  the  brace  inaxes  v/ith  a  horizontr.  1  lir.e  be  represented  by  .       O( 
then  the  total  stress  or  load  to  which  the  brace  is  subjected  will  be  represented 
by  T  =  pA  sec   ex  . 

If  the  excavation  is  made  v/ith  vertical  parallel  sides,    as    for  deep 

I       -  • 

sewers,  or  water  pipes,  the  expression  for  the  load  which  any  horizontal  brace 

must  carry  vail  be  identical  with  that  just  given  with  the  secant  of  the  angle 

made  gqual  to  unity.  The  expression  will  then  beco:::e  T  =  pA.  « 

The  timber  or  other  struts  which  have  to  be  used  for  the  purposes  in- 
dicated, are  then  to  fee  designed  under  appropriate  beam  rnd  column  formulas  with 
the  preceding  values  of  p  rnd  T  for  loads.  If  these  operations  are  performed  with 
judgment,  it  is  seldom  that  the  conditions  attending  the  work  cannot  be  sr.fely 
and  economically  controlled. 

EFFECT  OF  COHESION 

The  usual  formulas  for  earth  thrust  consider  solely  the  weight  of  the 
viaterial  and  the  force  of  friction.  Thus  surfaces  of  cleavage  or  rupture  are  con- 
sidered plane.  As  a  .natter  of  fact  due  to  the  combined  action  of  friction  and 
cohesion,  these  surfaces  are  warped.  When  cohesion  is  neglected,  pressures  exerted 
appear  larger  than  they  rctually  occur  in  nature.  Thus,  a  formula  like  that  by 
Bankine  gives  results  on  tie  safe  side,  often  entirely  too  conservative. 
Fig.  36a  gives  tie  solution  to  *he  follow  ing  problem: 
Consult  "Earth  Slopes,  Retaining  "/alls  rnd  Dams"  by  Charles  Prelim, 
TO-  1  -  27,  Given  a  bank  of  homogeneous  earth  25  ft. 'high  whose  cohesion  is  110# 


108 

per  sq.  ft.  Take  $  -  30"41'.  Consider  horizontal  sections  at  intervals  of  5  ft. 
By  Prelini's  method,  pp.  15-17,  determine  (a)  the  proper-  stepped  slope  for  this 
material,  (b)  the  slope  of  equal  stability. 

Embankments  along  streams  often  show  a  frash  break  of  er.rth  v/ith  an 
overhanging  top,  as  shown  in  Fig.  36A,  at  the  point  C.  7/ith  w  sathering' the  upper 
portions  of  material  will,  grr.dur.lly  break  away;  thus  the  earth  slope  AEC  is  not 
stable  except  for  limited  periods. 

VThen  Irrge  excavations  in  Civil  Engineering  .n*  Mining  practice  are  nr.de 
for  temporary  worlc,  sheet  piling  or  other  bracing  :i?.y  be  omitted,  provider  tho 
ground  is  stepped,  as .shown  in  the  fi'gire.  In  this  way  considerable  quantities 
of  excavation  can  be  saved  above  the  slope  AE  which  fires  the  angle  of  repose. 
To  what  extent  these  steps  and  berr.is  may  depart  from  the  plane  of  rupture  and 
approach  the  slope  of  equal  stability  for  fresh  earth  is  dependent  upon  the 

degree  of  safety  desired  rnd  the  length  of  time  during  which  the  excavation  is  to 

> 

remain  unbraced = 

On  page  37,   Chapter  2   of  these  notes,  reference   is  r.ade  to  an  article 
on  "Earth  and  Rock  Pressures"   by  E.   G.  Moult on,   Trans.  Am.   Inst.  Dining  Engineers. 
Feb.    1920.    This  paper  gives  an  excellent  account   of  the   limitations  of  the  classic 
earth  pressure   formulas.    It    is  now  well  loiown  that   in  deep  trenches  the  greatest 
thrusts  do  not  always   exist  at  the   bottom  of  the   excavation. 

In  Fig.   36B  x  represents  the  depth  in  feet  of  a  trench  where  materials 
are   retained  by  sheet  piling  and  bracing.    In  his  article  Moult on  explains  that 
the   line  of  rupture  approximates   the  curve   shown;   the   surface   of  rupture   inter- 
cepting the  ground  level   about  x/2   ft.   back  of  the  vertical   through  the   lowest 
-:>oint   in  the  trench.    If  the  sheet  piling  tends   to   give,  the    earth  moves  along 'the 
line  of  rupture,  but  due   to  the   forfies  of  cohesion  rnd  friction,  arch  action  Is 
induced,  as  shown  in  the   figure,   giving  maximum  thrusts  agr.inst  the   sheet  piling 

» 

in  the  vicinity  c\f  the  horizon.     .  AA,   rather  than  at  the  bottom  of  the   trench. 

Experience  hrs  aicvn  that    frequently  the  nerviest' bracing  is  needed  at 
such  a  level  as  AA  and  nobracin-  fit  all  at   the   bottom  of  the  pit.   V/ere  the  usual 


109 

formula   for  earth  thrust   followed,   the  bracing  would   increase  in   size  and   strength 
with  the   depth  of  trench,    thus  using  the  material  uneconomical!;7  and  improperly. 

These   observations  apply  v/ith  particular  force   in  mining  and   tunnel  con- 
struction,   Such  properties  of  granular  masses  are  not   limited  to  earth  and  sand, 
but  apply  also  to  lurolcen  rock,   to   stored  grain,   coal  piles,   etc.    The  student  is 
urged  to  read  ivloul ton's  article;    referring  particularly  to  his    fig.    14,  pp.    22-25 

ELAVY  r/OODEM  SHEET   PILING 

Excavations   for  bridgepiers  are  frequently  r.irde  in  saturated  material 
sometimes  covered  by  shallow  water;   see  Figs.   38  and  39.    In  such  cases   it   is 
necessary  to  use  the  heaviest  class   of   sheet  piling  consisting  of  6  x  12,    10  x  12 
.or  even  12  x  12   inch  sticks,   driven  by  an  ordinary  pile   driver.  These   sheet  piling 

sticks  are  usually  tongue-and-grooved,    some  tines  by  working  them  into  the  required 

or  4 

shapes   or  more    frequently  by  spiking  2  x  Scinch  strips  to   the'  10  or   12   inch  sides; 
see  Fig. 38. 

Various  types  of  what  may  be   called  c  ompound   sheet  piling  are  formed  by 
bolting  or  spiking  together  3-12"  planks  2,   3  or  4   ins.    in  thickness,    so  as  to 
.tirke  the  two   outer  ones  overlap   the  middle   one  by  2  or  3  inches.    The  '.Vakofield 
sheet  piling,   Fig.   32  is  perhaps  the  most  prominent  example   of  this  type.   It  has 
bec-n  much  used  v/ith  very  satisfactory  results;   cf.    "The  Cofferdam  Process   for 
?iors"  by  C,L. Fowler;    for   other  types,   Fig.   38,  p. 60.    One  of  the   difficulties 

:cperienced  in  deep  driving  of  this   nervy  sheet  piling  is  the  "wardering"   of  the 
';owor  points  of  the   individual  pieces.    In  spite  of  the  greatest  crro,  the   lower 
edge   of  the  resulting  sheeting  mry  be   found  much  out   of  lino,  giving  the   completed 
i-heetirnj  a  warped  shape,    inducing  t/.o   opening  of  joints  and  l^alcrge   of  water  into 

-ho  excavation  as  the  work  progresses. 

i         In  those  cases  of  horvy  sheeting  for  bridge  piers,  the-  volume  of  oxcava- 

ion  must  be  made  larger  in  plan  by  1  1/2  to  2  or  5  ft.  on  each  side  then  the 
lass  of  masonry  which  is  to  be  built  within  it,  f or  t ho  purpose  of  giving  the 
'ocuisite  room  for  the  wrling  pieces  and  for  the  mesons  in  their  operations  of 

aying  masonry,   should  the   latcer  be   other  than  concrete;   see   distance  a  in  Fig. 39  . 


If- 

;7here   the   footing   is   of  concrete,    or  where   the  entire    :rss   of  masonry  is  to  be 

of  concrete, -^s _.  •  ,; .      ,-the  entire 

volume  between  the.  sheeting  is   filled.  The  concrete   is  placed  jn  layers   of  9   to   12 
ins.    in  thickness  reaching  the   sides  of  the    sheeting,  and   thoroughly  rcnrned,  as 
required  for  such  work.    The   timber  braces  /iiay  be  takon  out  as  tho  masonry  progresses 
leaving  the  sides   of  the  sheeting  braced  against  tho   completed  -portion  of  the  pier. 
Dr,    if  the  volume  is  filled  7/ith  concrete,    the  timber  bracing  which  vill   be  per- 
manently saturated  with  water,  may  b  o   left  in  the  concrete  mass.  All   timber  bracing 
however  which  will  not  certainly  be  saturated  should    be   taken  out   before   the  con- 
crete  is  deposited,    leaving  the  concrete   itsolf  to  hold   the   sheeting  in  piece. 

When  the  plan  for  the  excavrtion  for  a  pier  lias  been  so  laid  out  at  the 
site  rs   to  lerve   sufficient  clear  spree   inside  the  sheeting  to  meet  the  require- 
ments above  d  escribed,  a  line   of  shoetir.3  is  driven  usually  by  a  pile  driver 
around  the  entire  enclosure,   the  tongue   of  each  individual  piece  fitting  closely 
into  the  groove  of  the  adjrcont  piece,   as  shown  in' Figs.   38  and  39.   The   lower  end 
of  arch  piece  should  bo   so  fooveled  as  tocrov>Td  it  closily  against  its  neighbor  in 
driving.  At  this  .beveled  end  a  thin  shoulder  of  the    full  section  of  the-  original 
piece  should  be   left   so  as  to  partially  or  wholly  close  the  triangular  opening 
which  \vould   otherwise -afford  unobstructed  entrance  for  water,  mud,    sand  or   other 
flowing    laterial.   This   detail  is  shown  in  Figs,   38A  and  38B.   After   the-  sheet 
piling  is  driven  to  the   desired  depth   so  as  to  enclose  the  site  to  be  occupied 
by  the   foundations  and   to  b  e   as  nearly  vr.ter   tight  aspossible,    the  material   en- 
olosed  is   to  be  excavated.    If  it   is  sufficiently  soft,    it  may  to  some  extant  be 

Iredged,   but   it   is  usually  taken  out  by  .hand,   thrown  into   large  buckets,    lif 

• 

>ut  by  power  and  either  spoiled  on  ^.ste  land  immediately  adjccent  or  convoy* 
)thor  points  by  land  or  water,  As  fast  as  the  excav;  tion  is  maOe,  heavy  horiaoi 
v/aling  strips  are  put  in  plrce  and  properly  braced  across  the  entiie  pit,  or  around 
itif  the  excavrtion-  is  polygonal  or  of  curved  outlines,  so  that  the  sheet  pill* 
,ay  not' be  forced  inward  by  the  pressure  of  the  outer  material.  These  waling 
,ieces  (10x12,  or  12x12  in.  .ieces  in  heavy  work)  «st  be  placed  closer  together 


111. 

verticr.lly  as  the  excavat i on  proceeds,  as  the   inwr.rd  pressure  of  the   surrounding 
.vater  ial   increases  with  the  depth  in  the  manner  shown  by  equations  1  and  2,    The 
sizes   of  the  brr.ces   (and  of  the  waling  pieces  also)   are  to  be   designed  as  carrying 
the   loads  described  in  connection  with  the  derivation  of  equations   1  and  2,    it 
being  remembered  that   in  these  crscs  the  retained  •nateriril   v/ill   in  nerrly  or  quite 
alTcases  be  saturated  with  water.    If  the   ercavtion  is  rectangular  in  plan,  the 
corners  must  be  braced  with  diagonal  sticks  suitably  placed  and  s  tror.gly  held  at 
the  ends.  Again,    if  the   length  of    the  excavation  is   so    ;;ro:.t  u  hat   it    is  inadvisable 
to  b  race  with  single  pieces   of  corresponding  length,    special   trussing  or   brr.cing 
must  be  provided,   particularly  at  the  ends,  or  a.  t  polygorial  corners  as  indicated 
in  Fig. 38,  which  shows   the    plans   of  a  piece   of  work  of  this   chrracter  as  actually 
constructed.  The  tiers   of  horizontal   bracing  may  be  placed  as  much  as   6  to  8  ft. 
apart   at   t:  e  surface,  but  at  a  depth  of  30  to  55  ft.    it  ::ay  be  necessary  to  place 
them  only  3  or  4    ft.    apart  verticr.lly.   Za:cavations  have  been  carried  to  depths 
of  over  40  ft.   by  this  method,   bu'c   unc'er  such  circumstances,    the  utmost  vigila.nce 
and  continuous   care  must   be  'exercised  in  order  to  properly   guard  against  accident 
or  failure.   The  work  should  be  prosecuted  with  c  he  greatest  rapidity  consistent 
with  suitable  safety  precautions    in  order  that  the  period  of  risk  may  b  e  reduced 
as  much  as  possible. 

In  all  such  work  it   is  usually  necessary  to  l.:eep  pumps  constantly  at  v/orlf 

in  order    to  -naintain  the  excavation  so  nearly  free   of  water  rs   to  afford;,  opportunity 
for  the  requisite  excavation.    It   is  not   frequently  necessary  to  coTuience  pumping 

.     * '~; 

until  a  considerable  depth  of  e  ;:.cavation  has   b--en  re;ched,    but  as  the  greater 
depths  ara  attained,  t  he  wrter  is   so/.ieti.nes  exceedingly  troublsso^e.    The  tongue 

v- 

and  gnuorve  detail  of  the  piling  and  the  driving  of  the  latter  solidly  down  on 
the  rock,  or  other  hard  bottom  so  as  to  broom  the  points  of  the'  piles  into  as 

many  of  the  s.nall  openings  as  possible,  are  designed 'to  .;ake  the  enclosure  as 
r.ecrly  water  tight  as  practicable.  Rotary  pumps  v/ith  their  freedo.n  from  valves 
.re  ac..urc.bl"  rdapted  to  such  puniping  as  it  is  required  in  these  crses,  inasmuch 
s  the  water  carries  much  solid  matter, 


o  tj  -;:£•  IT 


- 


112 

« 

After  the  rock   has  been  laid  bare  by  this  process,    it  is  to   be  thorough- 
ly cleaned  off  before  any  masonry  is  put   in  piece.    Then  all   soft  or  other  un- 
satisfactory rock  should   be  carefully  and  completely  removed.   If  the  surface  of 
the  rock  is  sloping,    it  should  either   be   stopped  off  roughly,   or  made  rough  and 
jagged  if  it   is  not  naturally  so.   Those  operations  must  be   completed  with  care 
in  order  that   the   footing  course  of  concrete   or  other  masonry  <r>ay  be  satisfactor- 
ily bonded  to   the  rock.    If  the   resultant  thrust  on  the  rock  is   inclined,   as  in 
the  case  of  an  abutment   for  an  arch;,   then  the  preceding  operations  can  tee  sp 
applied  as  to  make  the    foundation  bed  at   least  npproxi:na.tly  normal  to  the  direction 
of  the  thrust.  After  the   foundation  bed  has  been  thus  prepared,   the    footing 
course  of  concrete   or  other  masonry  can  be  put  inplace.  \7hi2e    this  is  beirg  done 
the  water  which   finds   its  way  into   the  enclosure  should  be   led  by  suitable  drains 
to  a  sump  at   so  ;ne  point  within  the   excavation,  from  which  it  mus,t  ba  pummtad  in 
order  that    the  footing  nasonr^r  may  be  built  up  dry. 

Fig.   39  gives  diagrammatically  an  example   taken  from  actual 

-practice  showing  a  use  to  v/hicli  sheet  piling  mr.y  be  put.  The  rectangular  enclo- 
sure is   21   ft.  x  64  ft. 5  ins.,    leaving  a  clearance  "a"    for  bracing  rnd  workmen. 
The   figure  describes  an  approach  pier  founded  on  piles  driven  in  mud  and  silt 
overlying  bedrock  at  a  considerable  depth.   The  pier   is  in  two  parts,   to  save 
•masonry.    It  supports  deck  latticed  approach  spans   for  a  large  city  highway 
bridge.    The  sheet  piles  with  pumping  kept  back  the  flow  of  s  ilt  into  the  exca- 
vation and  reduced  ths  water  lovel  within  the  enclosure  so  that  the  mud  and  silt 
could  be  excavated  to   elevation  -  14.0,     A  layer  of  sand  1   ft.  thick  was  trmped 
upon  the   finished  mud  surface.    The  piles  were-   cut  off  rt   elevation  -10.0,   A  slab 

• 

of  concrete  3  ft.    thick  deposited  upon  the  srnd   layer  formed  a  plane   surface 
for  the   completed   enclosure  upon  which,   in  the   dry,   the   two  component  pier  courses 
were  built,   first- three  steps  o-f  concrete,    then  a  fertuiewith  limostoie   front 
followed  in  turn  by  granite  as  I",  lor  for  t  ho  upper  visible  portion  of   ti.e  pier  and 

co-oings.    In  work  like  this,    rt   lorst  for  appe:ranco,    the  s  heat  piles  ?hould 

• 

finally  be  cut  off  below  the  pernanont   low  tide   or  water   level  before  backfilling 
asrainst  the  ~Dicrs. 


113 

STESL  SHEET  PILING- 

Recently  a  distinction  has  been  made  b  etween  "sheeting"  and  "sheet 
piling".  Mr.  J.  C,  ;,Ieem;  Trans..  A~,i.  Soc.  C.L. ',  Vol.  60,  p.  1,  defines  "sheeting" 
as  that  class  of  sheathing  which  is  set  or  driven  coir.-eidently  with  tn.:e  excavation 
and  "sheet  piling"  as  that  class  of  sheathing  v:hich  is  driven  aher.d  of  the  excava- 
tion or  beyond  its  find  limits.  This  article  deals  only  with -sheet  piling. 

ill-.  P.  B-  V/oodworth;  Jrr.ns.  ^.:ioSoc.  C,L.  .  Vol.  64,  p,  47^,  gives  an 
interesting  historical  review  oi  the  use  of  piles  a.nd  sheet  piling.  V,ood  was  used 
for  these  purposes  ir:  the  er.rli-eut  historical  tii.-es.  \\ooden  sheet  piling  is 

li.iited  in  length.  It  w  ill  stand  little  abuse  front  he  pila  driver;  it  cannot  be 

^ 

driven  into   stiff  ."aterials;    it  cm  be  used  only  once;   it  cannot  be  .ir.de  to   inter- 
lock v/ell  and   therefore   does  not    insure  water  tightness.    Its  joints  are  werlc; 

• 

its  span  cannot   be  large  horizontally  or  vertically;   consequently  it   requires 
much  interior  bracirg  for    large   excavr t i ons „   It   is  to    be   suspectscl  theLefore  that 
rnetal  sheet  piling  v.'.?.s  thougl:t  of  in  the  past   though  it  hrs  become   coriTiercially 
practical  only  in  the   la  st  decade,   ;-.u  .  '.."ooovorth  describes  early  for. ns  of  c  ast 
iron  sheet  piling,    one  type  by  ifc,t thews,   1822;   another  by  i'eter  Btvcrt,   1822; 
others   by  Janes  Y/r  liter,   1824;  \ia.   Cuoitt,    1832;    he  gives  also    SOMO  later  examples. 
See  also  Appendix  VI,   to  Ordinary  Foundations,  by  C.E. Fowler. 

Cast   iron  is  an  unsuitrble  v.r.terial.;    it   is   brittle   in  driving,    it   cannot 

stard  high  bending  strains-    Seventy  years  ago  it  cost   more  tb-.n  wood,   prrticularly 
in  this  country  v/here  wood  \z.s  plentiful.  \.Tlnber  is  now  a  scarcer  a  rticle  a.nd 
rolled    :.,etcl   shapes   less  costly  than  they  were  20  years  rgo.   Steel   is   tough v  r.nc"1. 
fitted  for  driving  through  stiff  :.ia.teri:.ls.   Sheet  piles  of  steel   i-.r.ybe  rolled  to 
give  strong  joints  end  reasonable  water  tightness .  .V/ood  sheet  piles  cannot  be 
used  a   second   ti.;e.   Liodern  sieel  sheet  piling  car.  be  pulled  :nd  redriven,    On  a 
sewer  trench  at   £u.;irdtv   i-ev/  Jersey,   "100  lin.    ?t.    of  10  ft.  We.nlinger  corrugrted 
sheeting  vr  s  used  on  8000   ft.    of    sewer  in  a  trench  varying  in  depth   from  9   to  & 
ft,;    thr.t   is  to  say,    the  sa..ie   sheeting  wr  s  driven  and  pulled   at  least  80  tines  and 
at  the   co^ole-cion  of  the  job  was  still   in  good  condition,   This  sheeting  was  made 


114 

of  16  gauge  mr.terirl,  v/eighing  5  Ibs.  per  sq.  ft.  in  place".  Other  examples  could 
be  cited.  Steel  she:-t  pilesof  heavy  rolled  sections  car.  be  driven  readily  through 
obstructions.  Instr.nces  are  not  uncommon  where  they  have  been  driven  successfully 
through  buried  logs  or  railway  "ties  or  into  compact. hardpan. 

REQUIRE E'.  IS  FJK  :,IB2Al  PILING-. 

1.  Strength,  2.  stiffness,  3.  water  tightness,  4.  economical  and  prrctical 
sections,  from  manufacturers'  standpoint. 

Fig.  40  shows  a  variety  of  sheet  pile  sections  now  used  in  pr:ctice. 
Consult  article  by  II;: .  L.IL  Clifford,  Trrns.  ^m.  Soc.CoS.  ,  Volo  64, p. 441.  Ke  arranges 
these  sections  into  three  groups:-  1.  standard  structural,  shapes;  2.  special 
rollsd  shapes,  3,  specirl  shapes.  It  crnnot  be  argued  that  Standard  rolled  shapes 
are  necessarily  the  cheapest,  The  cost  of  sheeting  per  sq  ft.  in  place  is  the 
governing  factor.  This  'frctor  depends  Upon  the  ease  with  which  a  specir.l  type  may 
be  driven  into  a  given  ..rvceri:  1  and  upo  ••  the  effective  v/idth  per  sheet  pile  v.-hen 
interlocked.  In  sane  designs  the  interlocking  devices  consume  mueh  of  the  gross 
v/idth  of  ar>  individual  pile.  Begulai'  rollsd  shapes,  group  2,  require  riveting; 
v/Iiile  specirl  rolled  shapes,  group  2,  eliminate  shop  work  and  give  a  simple  inter- 
locking ferture.  Corrugrted  piling,  group  3,  is  expensive  per  Ib.  of  metal,  but 
usually  is  cheap  per  sc,  ft.  in  plr.ce.  "'here  water  tightness  is  d  eraanded ,  the 
type  of  piles  should  be  selected  irrespective  of  cost  per  Ib.  of  ,netal.  The  pile 
with  -che  tightest  joint  should  govern. 

Metal  piling  .mst  resist  two  groups  of  stresses;.  1.  bending  stresses 
due  to  earth  or  water  pressure,  2.  shear,  bending  and  tension  in  the  Interlocking 
joints.  Steel  sheet  piling  usually  it,  braced  at  the  top  and  bottom  only,  For  deep 
work  there  nay  be  intermedia ;e  waling  sticks.  One  disadvantage  of  netal  sheet 
piling  is  the  difficulty  in  fastening  waling  sticks  r. rd  other  interior  bracing. 
Ecuations  1  and  2  determine  approximately  the  lord  intensities  producing  bending 
for  verticrl  spans  b  etween  waling  st:ips.  The  section  modulus  should  be  ".s  great 
as  possible  for  weight  of  metal  p?r  lineal  ft.  of  pile.  The  metal  massed  at  the 
sides  for  interlocking  purposes  should  help  to  give  the  greatest  section  modulus  - 


115 

Strictly  a  single  pile  does  not  act  clone  in  bending.  Adjacent  piles  support  each 
other  through  the  interlocking.  Therefore w e  must  canpute  the  section  modulus 
per  lineal  ft,  of  width  of  piling  interlocked  in  pt.ce. 

The  piles  should  be  sufficiently  stiff  to  drive  without  buckling  or 
crushing,  and  particularly  without  springing  under  the  blows  of  a  hammer.  The 
radius  of  gyration  relative  to  the  pile  length  should  be  as  large  as  possible 
for  a  given  weight  of  metal  in  the  pile. 

To  secure  water  tightness  attempts  hr.ve  boen  Mace  to  p?.cl:  or  caulk  the 

• 

joints  with  wood  strips  or  other  in;itorials.  That  type  of  piling  nay  be  considered 
the  best  which  requires  no  such  packing  in  the  interlocking  joints.  Indeed  prac- 
tice shows  that  it  is  impossible  to  do  any  effective  caulking.  7/hen  a  line  of 
piling  has  been  driven,  it  often  happens  that  it  re:r.ins  in  alignment  at  the 
bottom  and  bulges  gradually  to  the  maximum  displacements  at  the  top.  The  piling 
thus  offers  a  warped  surface _  toward  the  excavation.  Shearing  and  bending  stresses 
aswellas  tension  are  thrown  upon  the  interlocking  joints.  That%  type  of  inter - 
l^jjking  is  "best  which  will  resist  the  opening  of  joints  due  to  shear  and  t  ension, 
particularly  when  the  piling  bulges. 

The  chief  disadvantage  of  metal  sheet  piling  is  the  difficulty  in  fasten- 
ing waling  sticks  arc1,  other  interior  bracing.  Such  connections  can  be  made  more 
easily  to  timber  than  to  metal  cofferdams-  Again,  timber  sheet  piling  often  is  a 
fixed  portion  of  a  foundation,  For  parts  permanently  below  the  water  line  the 
timber  will b e  sound  indef initely.  Metal  sheet  piling  is  subject  to  corrosion. 
Considering  the  problems  of  bracing  and  the  cuestion  of  duirbility,  one  may  con- 
clude that  metal  sheet  piling  will  never  supersede  ant  ire  13'  the  us  e  of  timber 

SPECIFICATIONS  FOR  STEEL  SH_i,.:T  PILING 

Material.  The  steel  used  shall  satisfy  the  specifications  of  the  American 
Association  of  Steel  Manufacturers  for  Structural  Stenl  for  Buildings. 

Working  Stresses.  The  allow:  ble  unit  stresses  per  sq .  i:-..  on  extrene 
fibers  in  bending  shall  no-c  exceed;-  for  permanent  work  16,000  lb,,  for  temporary 
work,  20,000  lb.  The  section  modulus  in  bending  is  to  be  fi cured  for  interlocked 
piling  in  place 

St i f fne ss . Sirgle  piles  driver,  separately  shall  have  a  ratio  of  length  tt>  . 
least  radius  of  gyration  not  to  exceed  250. 


- 


116. 

x 

Water  Tightness.  The  sections  when  r. ssembled  in  piece  shr.ll  be  water 
tight  at  joints-,  without  the  use  of  auxiliary  packing  or  caulking  pieces,  unless 
such  packing  of  caulking  pieces  are  made  a  part  of  and  are  assembled  v.ith  the 
sections  of  the  sheeting  or  sheet  piling  before  driving 

Priving.  Care  shall  b  e  taken  in  driving  to  prevert  battering  of  the 
heads  of  the  pilas,  and  if  necessarv  to  prevent  this,  a  tight  fitting  cap  shall 
be  used.  Driving  shr.ll  be  done  by  steam  or  compressed  air  hammers. 

REIKFORCED  CONCRETE  SHEET  PILES. 
Recently,  for  heavy  and  durable  work,  there  have  been  proposed  or  used 

occasionally,  reinforced  core  rete  sheet  piles;  each  pile  nr.de  of  rectangular 

/ 

cross  section  with  grooved  ends  to  engage  special  keys  to  give  a  water  tight 

joint.   In  some  cases  the  piles  have  been  specially  molded  to  dovetail  into  each 
other.  Buel  &Hill,  "Reinforced  Concrete",  pp.  162-187,  illustrates  some  examples., 
among  others,  the  Hennebique  system,  Fig.  55.  Each  unit  pile  is  reinforced  like 
a  column  with  rods  or  structural  shapes.  Special  caps  are  employed  v/ith  a  false 

« 

pile  to  protect  the  concrete  pile  from  the  blows  of  the  hammer.  In  general,  the 
same  problems  are  presented  as  for  reinforced  concrete  piles;  this  subject  is 
treated  further  under  that  heading.  Reinforced  concrete  sheet  piles  must  withstand 
bending  strains  when  in  place,  also  shear  and  t  ens  ion  stresses  at  joints,  and  in 
addition  the s tresses  to  which  an  ordinary  pile  is  subjected.  Thus  far,  there  has 
not  been  a  large  field  for  the  application  of  reinforced  concrete  sheet  piling; 

but  its  use  is  daily  increasing.  It  is  expensive, 

^ 

HEME3IC.UE  SHEET  PILIl'S   -  Fig ,55 

This   form  is  adapted  for  heavy 'sheet  piling,   by  using  a  rectangular  cross 
section  5  7/8  x  15  3/4   ins.,,    reinforced  with  6  vertical  rods  tied  together  at  12 
ins.    intervals  by  wire   ties.    Semicircular  spaces  about  2  3/4   ins.    in  c.iameter  are 
left  along  adjoining  edges   ol  the    sections,  ^fter  the  piling  1-c  s  been  c.^i^sn  into 
place,  cement  grout  is   forced   into  these  key  spaces,   cementing  '&--s  -^.tei-it.l  to- 
gether and  firmly  uniting  the   sections  of  piling  into  a  monolithic  wall  tff  great 
strength.   Two   light  I-beams  have  sometimes  been  used  for  vertical  reinforcement 
in  place   of  the   6  circular  rods. 


— *>.  .     , 


REINFORCED  COHCHBTE  SHEET  PILING;  U.S.  NAVAL 
COAL  DEPOT,  TIBUEON,  CALIFORNIA 

Fig.  40A  illustrates  the  Cioss  section  of  pier  a.nd  coal  pockets.  Hrrd 
bottom  is  found  at  irregulr.r  deaths  rlong  the  pier  length.  Both  hr.rd  and  soft 
bottoms  slope  to  increasing  depths  rvfc  the  water  side.  The  coal  near  the  pier 
rests  on  a  timber  mat  at  elevation  +1  ft.  This  mat  of 'itself  is  incapable  of 
supporting  its  load  without  settlement.  The  pier  proper  therefore  no-t  only  sup- 
ports its  own  weight  but  resists  the  lateral  flow  of  the  mud  fill. 

The  pier  which  is  also  the  foundation  for  the  coal  bunkers,  has  a  40 
ft.  base.  Its  foundations  consist  of  wooden  piling  capped  with  12"  x  12"  K  40' 
timbers.  At  the  rear  there  are  three  lines  of  batter  piles  to t rke  the  lateral 
thrust  produced  b-  the  weight  of  coal.  The  timber  grillage  is  covered  with  a  4" 
timber  decking  laid  continuous  over  the  capsl  On  this  deck  was  built  the  front 
and  rear  concrete  retaining  walls.  These  walls  at  intervals  are  widened  into 
piers  which  support  the  steel  coal  bunker  columns.  At  intervals  also  the  walls 
are  connected  b~;  concrete  diaphragms.  The  pockets  between  the  walls,  above  ele- 

4 

vation  +2.0  weie  filled  with  earth  to  elevation  +10.0.  The  remaining  volumes 
between  and  to  the  rear  of  piling  and  behind Ithe  reinforced  corc  rete  sheet  piling 
were  filled  with  soft  mud  dredged  in  "front  of  tl:e  seawr.ll.  This  soft  mud  fill 
extends  to  elevation  +2..®  ft.  The  harder  foundation  bed  material  into  which  the 
piles  were  driven  occurred  at  depths  of  -  20to  -  35  ft.  To  hold  the  mud  fill  and 
soft  original  bottom  from  flowing  out  into  the  channel  produced,  the  necessity  of  a, 
continuous  he.  vy  reinforced  concrete  sheet  piling. 

EXTRACTS  FHOLI  THE  SPECIFICATIONS..' 

The  concrete  shall  consist  of  1  cement,  2  sand,  and  4  broken  s£one,  to 
pass  a  3/4"  to  1  3/4;i  ring,  Each  concrete  pile  sh:  11  be  cast  in  a  separate  and 
distinct  form  of  sufficient  stiffness  to  hole1  the  concrete  true  to  shape.  The 
forms  shall  be  water  tight;  their  surface  in  contact  with  concrete  perfectly 
smooth.  The  platform  upon  which  the  piles  are  cast  and  cured  must  be  a  rigid 
plane.  Reinforcing  rods  shall  be  accurately  spaced  and  located  a.nd  proper  means 
taken  to  insure  them  against  movement  after  having  been  properly  placed.  The 
concrete  for  er  ch  pile  shall  be  mixed  and  deposited  continuously  in  order  that  the 
•nost  perfect  bond  may  be  secured.  Concrete  shall  be  thoroughly  worked  around  all 
reinforcing  rods,  The  upper  free  of  the  pile  in  the  for.-.F  shall  be  cr  re  fully 
smoothed  off  by  trowelling.  If  -necessary,  in  order  to  s^c^ra  a  smooth  surface,  a 


Ill 

coat  of  mortar,  I  cement  to  2  sand,  shall  be  applied.  The  pile  for/as  shall  remain 
in  place  at  least  24  hours.  All  forms  must  be  thoroughly  cleaned  for  each  casting 
and  coated  with  crude  oil  or  other  approved  In.bricrtion  oach  time  the  forms  are 
used.  Concrete  piles  must  be  protected  from  the  direct  r;.ys  of  the  sun  $nd  kept 
damp  by  proper  covering  and  sprinkling  for  at  least  one  v/eelc  after  casting. 

Piles  when  removed  from  tha  forms  and  v/hen  b  eing  placed  shall  be 
true  to  form  and  dimensions.,  perfectly  smooth.,  free  from  wind  and  all  defects 
which  affect  their  appearance  or  strength  in  the  fi'nishc-c1.  work.  Main  steel  rein- 
forcement, Fig.lOB,  shall  consist  of  6  -  7/8"  round  bars,  located  as  shown, 
continuous  throughout  the  length  of  t?-e  pile;  these-  bars  to  be  braced  by  3/8" 
round  steel  clips  or  bands  at  24"  centers.  For  tha  top  5  ft.  of  the  pile, 
surrounding  the  6-  7/8"  rods,  provide"  reinforcement  equivalent  to  expanded 
metal  No.  10,  3  in.  metal.  This  reinforcement  shall  b e  bent  into  a  rectangular 
form  around  main  bars.  The  main  bars  shall  protrdde  4  in,  at  the  top  of  the  pile, 
to  bond  with  the  pier  concrete.  Each  sheet  pile  shall  be  bolted  to  the  12"  x  12" 
wood  stringers.  For  this  purpose  holes  are  provided  in  the  pile," 

Note:  The  piles  v/ere  cast  on  their  side.,  no  mortar  v/as  required  to 
secure  a  smooth  finish,  since  the  concrete  could  be  worked  smooth  on  account  of 
the  small  size  of  the  stone  used.  The  concrete  was  poured  wet.  It  was  all  mixed 
by  hand.  The  forms  were  often  stripped  after  24  hours, 

EXTRACTS  FRO:J  THE  SPECIFICATIONS  FOR  PILE  SRIVII-IG, 

No  piles  shall  be  driven  until  a.t  least  30  days£ld,  Kone  shall  be  ^oved 
or  otherwise  handled  until -experience  has  proved  that  it  may  be  done  with  safety; 
(to  be  determined  by  the  Officer  in  Charge),  All  piles  seriously  injured  in 
handling  or  driving  must  be  abrndoned.  Piles  sSall b e  driven  by  water  jet  under 
high  pressure,  To  this  end  a  2"  diameter  wrought  iron  pipe  shall  be  cast  into 
the  pile.  Ilaximum  pile  lengths  shall  b  e  40  ft.  All  piles  shorter  than  this  must 
be  driven  to  refuse:!.  To  b  ring  piles  to  final  position  only  light  short  blows  of 
the  hammer  shall  fee  used  with  a  proper  cushion  between  the  ;:>ile  and  hamnffir 
approved  by  the  Officer  in  Charge.  Pipe  ferules  cast  into  the  piles  for  the 
purpose  of  handling  them  past  be  properly  filled  with  cement  mortar  after  driving 
All  piles  shall  fee  driven  plumb  and  true  to  line.  They  must  closely  hug  the  12" 
x  12"  driving  stringer.  The  tongue  of  one  pile  shall  clo.sely  fill  the  groove 
of  the  next.  Any  pile  driven  so  that  the  adjacent  bearing  surfaces  on  piles  do 
not  come  together  within  3/4  in.  will  be  rejected.  The  pile  ,r;ast  be  removed, 
if  injured,  and  redriven 

Note: 'Piles  were  beveled  at  tlie  bottom-,  sse  Fig.  403.  Ho  piles  were. 
driven  under  30  days  ege.  Most  of  them  were  older.  At  first  the  2  in.  jet  pipe 
was  cast  into  the  pile  with  its  lower  end  chol-rsc.  to  a  bore  of  1  inch,  but  this 
jet  would  beco/.ie  stopped  as  the  pile  v/as  driven,  causing  the  hose  connection  to 
the  jet  to  burst.  This  interior  jet  proved  unsati&frctory  r.nd  its  use  was  dis- 
continued. In  its  -:>£.  ce  two  separate  jets  were  user1..  These  jets  were  hung  loose 
from  the  pile  driver  and  could  be  used  over  and  over  again.  Two  holes  Were  cast 
into  the  pile;  one  6  ins.  from  the  top  v/as  used  for  bolting  the  pile  to  the 
stringers;  the  other  IS  in.  lower  was  used  for  lifting  the  pile;  the  hole  6  in. 
from  the  top  not  being  strong  enough  for  this  purpose.  Very  little  trouble  was 
experienced  in  holding  piles  so  that  adjacent  bearing  surfaces  were  less  than 
3/4  ins/  apart.  Host  piles  were  driven  tight. 

Fig.  40B  shows  the  pile  as  designed.  A  number  wfs  so  cast,  but  after 
driving  a  few,  some  changes  v/ere  made*  In  the  figure  it  will  be  noticed  that  the 
bevel  at  the  pile  foot  is  on  the  same  si",  e  with  the  groove.  In  driving  the  tongue 


119 
of  the  pile  being  driven  fitted  into  the  groove"  of  the  pile  already  in  place. 

Tongues  stood  driving  better  than  grooves.  Therefore  when  failures  occurred 
during  driving,  it  was  usually  the  groove  of  .the  previously  driven  pile  that 
failed.  Consequently  two  pile<$  had  to  be  pulled.  G-enerally  the  groove  of  the  pile 
previously  driven  would  break  off  while  the  pile  juet  being  driven  would  be 
mninjured.  The  bevel  therefore  was  ch-:.nged  -co  the  tongue's  side;  Fig.  400. 

The  bevel  v/as  also  increased  but  to  too  groat  an  extent,  as  it  caused 
the  foot  of  the  pile  to  c  rowd  the  other  too  closely  at  the  bot'tom  so  that  after 
a  number  of  piles  were  driven  they  v;ould  not  be  plumb.  The  tops  would  lean  in 
the  direction  of  the  driving.  It  therefore  becane  necessary  to  bevel  some  piles  to 
a  slight  extent  on  the  opposite  side  just  before  driving.  It  is  believed  that  a 
bevel  intermediate  between  Figs.  403  and  40C  and  placed-  on  the  tongue's  side 
would  have  been  an  improvement.  The  bevels  on  the  pile  sides,  shown  in  Fig.  40B 
were  omitted  in  the  latter  design  of  Fig.  40C.  Side  bevels  seemed  to  make  the 
pile  drive  crooked, 

The  greatest  difficulty  in  driving  was  that  the  foot:of  the  pile  would 
go  out  or  move  av/ay  from  the  seawall.  The  concrete  piles ?  as  seen  in  Fig.  40A,N 
v/ere  driven  fairjy  close  to  the  wooden  piles.  The  woolen  piles  having  been  driven 
first  compacted  the  material;  therefore  when  the  concrete  piles  were  driven  their 
feet  would  tend  to  follow  a  line  of  least  resistance,  which,  wrs  awaj<-  from  the 
compacted  material  around  the  wooden  piles.  This  tendency  to  a  large  extent  was 
overcome  by  placing  the  jets  between  the  concrete  and  the  wooden  piles,  also  by 
beveling  the  concrete  piles  on  the  outer  side  only.  To  allow  for  ..lore  freedom  in 
driving  the  pile  tongue  was  nr.de  1/2  in.  thinner  than  as  designed.  This  allowed 
the  pile  to  give  more  without  breaking  a  groove.  In  only  five  or  six  cases  did 
the  head  of  a  pile  fail  in  driving. 

Two  v/ater  jets  v/ere  used  consisting  of  two  inch  pi£es  44  ft.  long 

connected  to  a  pump  by  fire  hose.  The  jets  were  usually  plrcec1.  one  on  each  side 
of  the  tongue  of  the  pile  already  driven  and  worked  down  as  far  as  possible. They 

v/ere  then  withdrawn  and  the  new  pile  set  in  place.  The  cushion  block,  follower  and 


•.  r 


120 
hammer  were  next  put  upon  the  new  pile.  The  jets  were  placed  one  on  each  side 

of  the  new  pile  and  worked  down  to  r. bout  3  ft,  in  advance  of  its  foot  when  the 
hammer  .started,  the  jets  being  worked  down  as  the  driving  proceeded.  The  cushion 
consisted  of  an  or.k  block  10"  x  14"  x  18"  with  rope  rind  rubber  hcs  e  nailed  to  the 
top  and  bottom.  The  oak  follower  was  placed  upon  the  cushion.  The  steam  hammer 
engaged  the  upper  end  of  the  follower.  The  bottom  of  the  follov/er was  cushioned 
with  rope  and  rubber  hose.  The  Steam  hammer  was  placed  in  a  special  frame  work. 
This  frame  work  moved  in  the  leads  of  an  ordinary  pile  driver.  The  frame  work 
was  necessary  since  the  leads  were  20  inches  wide  while,  the  piles  were  24  inches. 
The  pile  driver  was  placed  crosswise  at  one  end  of  a  barge.  At  the  other  end  of 
the  barge  was  placed  a  derrick  to  handle  the  piles.  The  sterm  hanraer  weighed 
6800  Ibs.;  its  moving  parts  3000  Ibs.  The  weight  of  a  40  ft.  'pile  was  7  £ons. 

Most  of  the  piles  were  driven  5  ft.  to  10  ft.  into  hard  material.  The 
specifications  stated  that  no  pile  longer  than  40  ft.  would  be  required.  Some  40 
ft.  piles  were  driven  with  great  ease  when  down  their  full  length.  The  depth  to 
mud  along  the  pile  face  is  -9.0  ft.  The  tops  of  the  piles  were  to  be  at  +3.0  ft. 
elevationj  thus,  28  linear  ft.  of  the  pile  penetrated  mud  and.  usually  3  ft.  or 
4  ft.  into  gravel  at  the  very  bottom.  The  wooden  piles  to  the  recr  of  the  concrete 
sheeting  drove  20  ft.  to  30  ft.  further  than  tl-.e  concrete  piles  in  most  places. 
'Some  concrete  piles  received  400  blows-  without  injury.  At  the  top  the 
piles  were  bolted  to  the  2  -  12"  stringers  vrith  1  1/2"  galvanized  bolts;  see 
Fig.  40A.  After  driving  the  tops  of  the  concrete  sheet  piles  presented  a  serrated 
outline  since  all  ^iles  did  not  drive  to  exactly  the  s. -me  elevations.  Expanded 
metal  was  placed  over  the  tops  as  shown  in  Fig.  40^-..  \Vhen  the  concrete  of  the  wall 
above  was  poured,  the  sheet  piling  and  wall  mrde  one  monolithic  mass. 

'  The  contract  price  for  the  piles  was  $2.00  per  lineal  ft.  delivered,  and 
60  cents  per  liner  1  ft.  for  piecing.  The  actual  cost  of  handling,  driving  and 
bolting  uo  tl:.e  piles  was  62  cents  per  liner. 1  ft.;  this  includes  labor  only.  9200 
lineal  ft.  of  "Diles  were  driven. 


.:'i    -    "  '-  ' 


121 

CONCRETE  SHEET  PILES  FOR  POCKS 

\ 

Recently  this  type  of  construction  has  been  repeatedly  recommended  for 
seawalls  and  docks  to  act  not  nerely  as  bearing  piles  but  also  to  eesist  the 
lateral  flow  of  ,nud  as  in  the  preceding  descriptions.  Consult  the  plans  by 
Haviland  &  Tibbetts  for  the  Richmond  Harbor  Project,  plates  6  and  7.  Examine  also 
a  report  by  Virgil  G.  Bogue,  1911,  on  the  Plan  of  Seattle,  plates  15,  16,  17/ 

AH  ANALYTICAL  PROBLEM 

Equations  1  and  2  hr.ve  been  .proposed  to  give  sufficiently  accurate 
d»ioul*t|oxiB  for  bending  stresses  in  both  v;ood  and  metal  sheet  piles.  Actually 
the  load  on  the  piles  is  variable,  increasing  in  intensity  linearly  with  the 
depth.  The  center  of  pressure  and  the  maximum  bending  moment  on  a  span  between 
waling  sticks  may  be  considerably  in  error  when  figured  by  equations  1  ard  2  for 
the  long  spans  ;nrde  possible  by  heavy  steel  piles.  The  following  study  is  proposed 
not  as  necessary  for  practical  designs  but  as  an  analytical  d  rill  for  t  he  student 
It  should  be  noted  that  the  treatment  is  similar  to  that  given  with  Fig.  34  for 
footings.  *.t  '• 

The  General  Case  ,  Continuous  Spans  ,  In  Fig.  41A,  let  AD  represent  a  line 
of  steel  sheet  piling  braced  by  v/aling  sticks  at  levels,  A,  B,  and  C.  It  is  re- 
quired to  compute  the  center  of  pressure  E,  and  the  total  pressure  P  upon  the 
span  1  between  ve.1  ing  pieces  B  anci  C;  also  the  position  F  and  the  mount  M0  of  the 
max.  bending  moment  in  the  span  1,  due  to  an  earth  pressure  of  intensity  p.  Since 
the  steel  sheet  piles  are  in  one  piece  from  A  to  D  there  is  continuity  at  B  and  C. 
The  span  1  has  fixing  moments  Mj_  and  Mg  at  these  supports  with  e  ffective  abutment 

shears  s  and  so.  To  simplify  the  analysis  assume  the  slope  of  neutral  curve 
1 

after  flexure  to  renain  vertical  et  B  and  C.  Equation  1  gives  the  pressure  in- 
tensity of  earth  at  any  head.  Consider  one  lineal  foot  horizontal  length  of 
piling.  Then: 


Pl  =  Whi   (1  -  sin  g[)    ,     p  =  W  (h^x)  &l-sin  $)      ,  p2  =  whp(l-sin  g)      .    .        .    (2) 
(1   +  sin  0)  fl+sin  0)  (1+sin  0) 

The  trapezoid  of  pressure   intensities  is   BGJC.   Again,    if  b  =  P2   -  j>i 


-f  •».-,. 


..        .•      - 

r<:;.r 


/r 


the  general  value  of  p  is:-     p  =  p±   +  bx  .............    .    .    .    .      (4) 

i 
Taking  momenta   about  B: 

,  s  I=h2-hl 

£m  =  /Px<lx  =    /  (Pi   +  bx)xdx  =  P!/|   (h2^}2  +   tog-Pi  )  (h2-^l)5  (5) 

0  ~FT~ 

From  a  summation  of  pressures: 

1  •    •    •    ...........    ................   (6) 


2 
Dividing  equati.  n(5)by(6)gives  the  value  of  m,    the  position  of  the  center 

of  pressure.  Equation  (6)  gives  the  magnitude   of  the   total  pressure   on  the   span  !„ 
Applying  the  equations  of  static   equilibrium  to  the  external   lords  acting 
up  an   the  span  1: 

s.i   +  s2  -  p  =  0   .    .    .....    .   .    .  ^    .    «   .    .    ...........      (7) 

i 

MI   -  M2   +  sgl   -  Pm  =  0   .    .    .    .    .    .    „    .    .    ,    .    ,     .    .    .    .......    (3) 

These  equations  7  and  8  contain  four  unknowns,  33.,  s2,  MI  and  ilg.  It  is 
necessary  to  establish  two  additional  equations  in  order  to  make  a  complete 
solution.  -The  extra  equations  .aey  be  established  from  the  elastic  conditions  which 

fix  the  slopes  at  3  and  C. 

, 

At  any  section  x,    the   equation  for  bending  moment  is'- 


El  d2w     =  Ml  -  sxx  +  /o'xi  dx  .......    o    ...........    (9) 

dx2"  6 

In  equation  9,   x  is  a  constant,  X]_  is   vari^ble  with  the   limits  o  and  x, 
p1    is  the  pressure  intensity  at  any  distance  ::]_   from  section  x.   Hence  w  is  the 
lateral  deflection  of  sheet  piling. 

p'   =  fi   +  b(x  -  a^).    ..............  ......    .(10) 

Substituting  the  value  of  p'    from  (10)    into    (9): 

/xl 
El   d2w  =  Ml  -   six  +/  /Pl+b(x-X]ll     xldx  =  Hl-six  +  pjx2     +  bx£,    .......    (11) 

dx2"  <f  ,  »  '  -^  —  6 

Integrating   (11)   between  the   limits  o  and  x  for  xi,   remembering  that  when 
x  =  0,,dvjF/dac  =  0: 


.-;...,  :;••:>.••>.•.-•••<. -"H; 

. 
•;X^::  i! 

•-.'.TS.-'VJ  i-'-Jf    ?  1 


*r  ^ 

/ax  r  I  I-  r 

BI  /    d2w     =  MI  /  dx  -  Sj_      /  xdx  +  f  i  /  x2dx  +  b_    /x^dx, 

^y     dx  />  "0  -2"  >6  6y0 

o 

El  dw     =  M]_x  -  SjX2  +  pix3       +  br.4  0    .    „    „    ......    o    ...    .    .    o    (12) 

dx  "IT"        -6  -  24 

Integrating   (12)   between  the  limits  o  and  x  for  X]_,   remembering  that 
when  x  =  0,  w  =  0, 


El  w  =  M-|_x2     -  six3  +  pTx4     +  bx5. 
-—        -—      ~2T~ 


120 
Jn  (12)  when  x  =  1,   d\v/dx  =  0;   in   (13)  when  •£  -  Ij,   w  =  0;  hence: 

0   -  MI   -  s.,1     +  pxl2     +  bl£.    o    ...    /   ..............      (  14  ! 

2  "T"  24 

0   =  Mi/2   -  Sll/6   +  pi!2/24   +  bl3/120   .......    ....    .....  (15) 

Equations    (14())  and   (15)   together  with  (7)  and   (8)  v.lll  give  completely 
the  ve.lues  of  s-^,    s2,  1.^  and  M2« 

The  shear  S  at   any  section  zn      is:- 

/JL 
'dx  =  &i  -   i    >  ?!  +  b(x  -  Z^U  dx  =  S]^  =  p^  -  bx2/2  ...      (16) 
J  ' 

TO  get  tlie  value  of  x,   for  the  section  of  maximum  moment  MQ,  place  s 
in  Equation  (16)   equal  to  zero   end.  solve   for  x  =  XQ. 


Placing  this  value   of  XQ   in  equation  (11)   gives   the  amount  of  MQ. 

Simpler  Case,    for  One  Continuous  Span.      In  many  cases  there    is  only  one 
span  1;  the  waling  piece  B  being  ct  the  ground  surface,  c  at  tije  trench  bottom; 

see  Fig.   41B.   From  (3),  pi  =  0;   p  =  wx  (1  -  sin  $}      ,   and 

(1  +  sin  0) 

P2  =  wH  (1  -  sin  gf).     ................    .......    (18) 

(    1   +  si  n  0  ) 


The  pressure  diasrem'    becomes  the  triangle  BJC. 
From  (4),   b  =  p2/H;  ?  =  bx  =  p2x/H  ....    .....    ............    (19) 

From  (5),  Prn  =  P2  H2  *  wH3   (    1  -  singf)      .    .    .    .    .    .    .....    „...,..    (20) 

~Z~         S      (1   +  sin  0) 

From   (6),    P  =  P2R/2  =  wH2/2    (1   -  sin  j\    ....   .....    .    .    .    .......    (21) 

(1+  sin  0) 


(•£-•• 


c ;, 


-  atjtf 


•     . 

- 


. 


124 

Hence  m  =  2H/3 ...... (22) 

From  (7)   si   -••  s2  -  P  =  0 (23) 

From   (8),  MI   -  M2  +  S2H  -  Pm  =  0   .   .    . .•'..' (24) 

From   (14),   MI   -  siH/2   +  p2H2/24  =  0 (25) 

From  (15),  Hi/2  -  siH/6  +  p2H2/120  •  0  ,-. (26) 

Combining  (25)  and   (26),   eliminating  si  end  solving  for  Ml9 

M,    =  P2H2/30  =  WH3/30   (1   -  sin  0)      ...............    (27) 

(1   +  sin  0) 

Taking  moments  about  bottom  waL ing  stick  C  for  all  external  forces, 
MI  -  M2  -  SiH  +  P(H-m)  =  0 (28) 

Combining  (25)  and  (28),  eliminating  si,  substituting  from  (27)  the 
value  of  Mj  and  solving  for  M2, 

M     =  p2H2/20  =  wH3/20   (1  -  an  0)      .    ...............    (29) 

(1  *  sin  0) 

From  (24),  s2  =  p2H/3  +  M2  -  MI   =  1/20  wH2  (1-  sin  gf)    .........  (30) 

*~1T~  (I    +  sin  0) 

From   (28),    s-L  -  p2H/6  -  Mg   -  MI     =  3/20  wH2    (1   -  sin  01     ..........    (31) 

H  (1  +  sin  (3) 


From  (17),   xg  =   +  Hi]  3/10  =  0.5477  H  . (32) 

From  (11),   we  get  MQ  by  substituting  the  values  of  Ml  frcfin  (28),    si  from   (31), 

«  =  V       s  -          :'._        -    .      ;     .'     -      '     -  -      .. 

M0  =  -  0.0215  wH3   (1   -  sin  gf)      .    .    ........'..........    (33) 

(1  +  sin  0) 

Practical  Case,  One  Simple  Span.  Where  bending  is  calculated  in 
practice  it  is  usual  to  assume  MI  =  Mg  =  0,  supposing  the  span  H  simply  supported, 
The  values  of  pi,  p2,  b,  P  and  m  remain  unchanged  as  given  by  equations  (18)  to 
(22).  From  (30)  and  (31) 

S2  -  p2H/3  =  v/H2/3  (1  -  sin  jj  ...................  (34) 

(1  +  sin  0) 

sl  =  P2H/6  =  wH2/6   (1  -   sin  0)      ...................    (35) 

(1   +  sin  0) 

From  (1C)   xo   =  ±  H/J1/3  =  0.577  H   .....................    .(36) 


125 
From  (11),  making  1^  =  0,    substituting  S]_  from  (35),  x  =  XQ, 

MQ   =  -  0.064  wfi3    (1   -  sin  gQ (37)  - 

(1   +  si  n  0) 

The  pressures  per  lineal  foot  against  the  waling  pieces  are  given  by 
equations  (34)  and  (35);  equation  (57)  gives  the  bending  moment  for  \vhich  the 
section  modulus  is  computed. 

ADDITIONAL  REFERENCES,   SHEET  PI-LI UG. 

1.  Steal  Sheeting  end  Sheet  Piling;   R.L.Gifford,  with  discussion;   Trans.  Affl.    Soc. 

C.E.  ,   Vol.   64,   p.   441,   Sept.   1909. 

2.  New  Systems  of  Steel  Sheet  Piling  with  Clamp  Connections;  Eng.  News,  Vol.  59. 

p.  133,  Jan. 30, 1908. 

3.  A  Practical  Treatise  on  Foundations;  W.M.Patton,  pp.  150-155;  Part  II,  Arts. 

6-9;  also  pp.  472  and  500. 

4.  A  Treatise  on  Masonry  Construction,  1. 0.  Baker,  10th  eel.,  p.  374,  1909. 

5.  The  Coffer  Dam  Process  for  Piers;  C.E, Fowler,  Arts,  IV,  V,  VI,  pp.  40-79. 

6.  The  Bracing  of  Trenches  and  Tunnels;  J.C.Heem,  Trans.  Am.  Soc.  C.E. .  Vol. 60, p. 1 

7.  United  States  Sheet  Piling;  Iron  i^ge,  IJay  28,1908. 

I 

08.  Steel  Sheet  Piling  for  Retaining  Earth  Under  Spread  Footings;  Eng.  Record, 
July  4,1908,  Vol.  58,  p.  15. 

9.  Experience  with  Steel  Sliest  Piling  on  Hard  Soils,  by  W.8.  Fargo;  Eng.  News, 

April  4,1907. 

10.  The  Strength  of- Sheet  Piling;  Eng.  Record,  Vol.  63  Apr.  1,1907,  'p.  368. 

11.  Eng.  News,  Vol.  59,  p.  133,  Vol.  63,  p. 117, 

12.  Drive  Inclined  Precast  Concrete  Slabs   for   Seawall;   Eng.  Sews -Record,   Vol.    81, 

p.    897.' 

13.  Notes  on  the  Design  of  a  Single  V/all  Cofferdam;  En~.  News-Record,  Vol. 82, p. 708. 

14.  Building  a  Sheet  Pile  Cofferdam  in  a  28  ft.   Tide;  Eng.  liev/s -Record,   Vol.    87, 

p,806. 

PROBLEMS 

1.  A  building  foundation  is   to  be  excavated  with  verticrl  sides  23  ft.   high 
in  a  sandy  loam  weighing  100  Ibs.  per  cu.ft.   and  standing  readily  on  a  slope  of 
1  1/2  H  to   IV.   During  construction  the  wells   are  ^supported  by  three  tiers  of 
vertical  woolen  sheet  piling  Jin  15  ft.    lengths  with  horizontal  waling  pieces 
spaced  10  ft.    vertically;   time  v/aling  piece   at   the    top.   Each  waling  piece  is 
braced  by  posts  spaced  8    ft.   horizontally;   and   inclined  st  an  angle   of  45*,v/ith 
the   vertical.   Design  the   light  sheet  piles   end  waling  sticks  as  simple  beams   for 
an  allowable  cross  breaking  stress  of  900  Ib.  per   sq.    in.    Design  the   inclined 


126 

braces  as  posts  by  the  column  formula  for  allowable  unit  stress,  s  =  1000  -  12  _!_ 

d 

where  g  is  in  Ib.  per  sq.  in.,  1  is' the  length,'  cr.d  d  the  least  dimension  of 
cross  section. 

2.  In  Fig.  36  compute  the  probable  axial  load  on  the  next  to t he  lowest 
inclined  brace  if  the  struts  are  spaced  10  ft.  laterally.  Suppose  the  retained 
material  is  wet  clay  mixed  v/ith  some  sand.  Us  sign  the  strut.  Y.'hat  pressure  comes 
on  the  waling  piece?  V.'hat  is  the  maximum  bending  moment  in  the  waling  piece? 
Design  it.  what  thickness  of  sheet  .piles  is  required  at  tris  level? 

3.  A  sewer  trench  is  to b e  excavated  15  ft.  deep  in  saturated  silt  weighing 
130  Ib.  per  cu.ft.  with  an  angle  of  repose  of  1  v.  to  4  H.  The  sides  are 
supported  by  Vertical  sheet  piling  vith  horizontal  waling  oieces  6,  6,  10  and  13 
ft.  from  the  surface,  braced  v/ith  horiac  ntal  braces  extending  across  the  trench. 

'  Design  waling  sticks  and  brcces  for  allowable  stresses  of  1200  Ib.  per  so.  in. 
of  either  cross  breaking  fiber  stress  or  direct  compression.  Use  standard 
sizes,  3"  x  6",  Or  6"  x  6",  of  timbers  throughout. 

4.  In  Fig.  38  compute  the  load  ona  horizontal  stirut  of  the  fifth  frame  from 
the  top  if  the  retained  roaterial  is  wet  river  mud.  Design  this  brace.  >7nat  is  the 
pressure'  per  lineal  ft.  against  a  waling  piece  in  this  horizon  of  bracing? 
Suppose  mud  may  rise  to  top  of  sheet  piles. 

5.  In  Fig.  39  suppose  that  the  concrete  slab  below  elevation  -  10  has  been 
placed  but  that  no  materials  of  any  kind  rest  upon  it.  If  the  water  surface  out- 
side the  sheet  piling  reaches  a  level  +2.0  and  has  free  access  beneath  the  concrete 
slab,  what  is  the  net  thrust  in  los.  per  sc.  ft.  tend!  n'j.  to  lift  the  concrete? 
\Vhat  is  the  average  total  pull  in  Ibs.  tending  to  break  the  bond  between  the 
concrete  and  one  pile  head?  V/hat  is  the  safety  factor  for  this  anchorage?  Neglect 
friction  against  sheet  piling. 

6.  A  building  foundation  is  to  '->  e  excavated  v/ith  vertical  v/ alls  10  ft.  high 
in  moist  loam,  weighing  112  Ib.  per  cu.ft.  with  an  angle  of  repose  of  1  V  to  2 
H.  The  sides  are  to  be  supported -by  sheet  piling  composed  of  standard  rolled 
steel  shapes  (channels  or  I-b-ams)  driven  far  enough  so  that  they  .nay be 
designed  as 'cantilever  beams  10  ft.  long,  fixed  at  the  bottom  of  the  excavation 
and  subjected  to  earth  pressure  computed  by  the  Rankine  formulas.  Design  with 
an  alloy/able  unit  stress  of  18  000  Ib.  per  sq.  in.  .a  " 

« 

7.  Suppose  the    sheeting  of  prob.   6  is  braces1,  as  in  Fig.  41B.  VJhat  is   the 
pressure  par  lineal    ft%   on  v/aling  sticks  B  and  C.   Design  them  of    Oregon  pine 
for   lateral  braces   spaced  8  ft.    centers  horizontally.   Compute  the  position  and 
amount   of  max.   bending  moment   in  the  steel  sheet  piles  for  ends    simply  supported. 
Design   the  sheet  piles  of  same   type  shown  in  Fig.   40  and   for  the  spa  cif  icr  tions 
given  in  the  text, 

8.  In  prob.    7  suppose  the  piling  tfonstraine  d  at  3  arJ.  C,  analyze  and  design 
in  parallel. 

\ 

9.    In  prob.    7,    suppose   the  sheet  pile  free  at  B  but  fixed  at  C.    Supply 
parallel  calculations  and  designs, 


127 

CHAPTER  6 

BEARING  PILES 
Introduction 

Where   the   soil  is  so   soft  that  it   is  impossible    or  impracticable  to 
obtain  sufficient  bearing  power  by  spreading  the    foundation,   or  whare  there  is 
danger  of  a    structure  being  undermined  by  running  water,   heavy  loads   frequently 
are  supported  upon  bearing  piles.   Cf.    Figs.   40,   24,   39  and  40A.  Hound   timber 
sticks  or  logs   are  most   common  for   this  purpose,   though  steel  in  special  forms 
and  lately /reinforced  concrete  are  used. 

The  supporting  power  of  piles  is   due  to  the.  friction  of    the  surrounding 
material   on  the    sides  of  the  sticks  r.nd  to   the  direct  bearing  power  of  the 
material  at   the  pile  points.    The  relative  value  of  these  two  portions  of  the 

supporting  capacity  is  extremely  variable,  but   the  former  is  usually  the   larger. 

) 

The  amount  of  this  friction  in  Ib.  per  sq.  ft.  depends  upon  the  kind  of  material 

penetrated.  Hard  compact  clay,  particularly  if  gravel  b e  mixed  with  it,  will 
permit  small  penetration  of t he  piles  only,  both  on  account  of  the  side 
friction  and  the  r  esis  tance  offered  to  the  point  of  the  pile.  At  the  ether  ex- 
treme, very  wet  mud  obviously  will  afford  little  side  friction  and  less  point 
resistance.  Between  these  "two  extremes,  all  degrees  of  side-  or  skin  friction  of 
the  piles  may  be  found  as  well  as  varying  degrees  of  point  resistance.  The 
latter  however  is  relatively  so  small  that  it  maybe  neglected,  except  in  those 
special  cases  where  the  point  of  the  pile  /neets  rock  or  other  hard  nr.terial. 

Many  tusta  have  boon  BO.C  with  piles  f or  t  ho  purpose  of  determining  the 
amount  of  side  or  dc in  friction  offered  by  the  material  penetrated.  As  -a  result 
of  those  tests  skin  friction  has  been  found  as  high  as  1850  to  1900  Ib.  per  sq. 
ft.  of  pile  surface-.  Those  high  fraluos  have  been  found  in  compact  clay  or  rnixod 
clay  and  gravel  or  in  alternate  strr.ta  of  dry  and  gravel  or  sand.  In  so  ft 
material  settled  sufficiently  solid1,  to  offer  satisfactory  pilo  support  frictional 
resistances  ranging  from  200  to  300  Ib.  per  sc.  ft.  have  boon  recorded.  Those 
values  show  that  the  surface  friction  of  tho  piles  will  vary  botween  wide  limits 


128 

for  material  which  may  bo  considered  s  atis factory  for  pilo   driving.    In  ordinary 
satisfactory  material,   with  hammers  varying  in  weight    from  3000  to  4000  Ib.    it   is 
probably  not   far  wrong  to  assume   a  skin  friction  on  the   surface  of  the  piles   vary 
ing  from  300  to   500   Ib.   per   sq.    ft.    Those  values   hrve   been   found   for  piles  driven 
from  10  to   20  ft.    in  the    stiffcr  materials   named,   and   from  40  to  (70  ft.    in  soft 
material.    Tho  value  of  the   skin  friction  will  bo  materially  increased  when  a   few 
hours  have  elapsed  after  the   completion  of  driving.   The  surrounding  .Tutorial   then 
has  an  opportunity  to  settle   firmly  into  all  tho  uncvcnncssos  of  the  pile  surface 
and   the    frictional  resistance  will  be  much  increased  over  that  which  exists   im- 
mediately subsequent  to  the    last  stroke   of  the  hammer. 

When  piles  are  used  for  building  foundations  they  commonly  are  driven 
into  compact  .material  such  as   sand,   hard  clay  or  hardpan,    in  which  cases  the  direct 
bearing  power  of  the  point  may  be  considerable,   although  it  cannot  be  accurately 
estimated.   Such  quantitative  tests  as  have  been  made   show  that  this  direct  bearing 
power  may  be   taken  fro.n  40  to   100  Ib.  per  sc  .in.   of  tho  nor;.E.l   section  of  tho 
pile  at   its  point.   Analyses  for  the  carrying  power  of  piles  have  been  made  by 
Weisbach.    Rankino  and  numerous  later  authorities;   all  analyses  however  are  based 
upon  assumptions  whicji  arc  only  approxi  lately  realized  in  practice  and  they  omit 
necessarily  considerations   of   some  of  the  complicated  conditions  which  surround 
the  penetration  of  all  piles.    Tho  best   compilation  of  those   formulae  is  that 
entitled  "Bearing  Piles"   by  Rudolph  Horing,  published  by  Enginooring  Hews  Pub. 
Co.   Lr.tcr  discussion  of  the   subject  will   bo  found  in  "Trans,  ^m.   Soc.    C,E.    for 
August   and  Nov.    1892.   No  purely  ideal   or  theoretical  c  onsidorctions  crn  be  imde 
to  give  accurate  values   for  the   sustaining  par;  or  of  piles;  but  such  considerations 
may  and  do  load  to  formulae  having  much  rcr.l  value  although  they  cannot  bo  depended 
upon  under  all  circumstances  and  may  even  bo  only  loosely  approxL--.ae.to  under  s  ome 
important  conditions   of  actual  work.  Tho  "Engineering  News   Formula"  appears  to 
fulfill  the  general  conditions   as  well   as  r.ny  formulr   yet  proposed'. 


129, 

TIMBER  PILES  -  TIMBSBS  AVAILABLE. 

Tho  principal  timbers  for  piles  along  the  Atlantic  Const  are  spruco, 
yellow  pino,  white  pine,  Norway  pine  and  oak.   On  the  Pacific  Coast,  Oregon  pine, 
or  Douglas  fir,  is  much  used.- In  the  interior  portion  of  tho  country.,  t.i\-j  'timber 
of  satisfactory  resistance  which  will  afford  sticks  of  requisite  length  and  stri  ight- 
ncss  is  employed.  Piles  may  be  of  alr.ost  any  diameter,  not  too  s;rall,  cut  from 
trees  v/hichgrow  of  sufficient  length  and  aro  at  least  fairly  straight.  They  arc 
of  all  lengths  up  to  80  or  90  ft.  and  usually  arc  specified  to  be  straight,  sound 
sticks,  free  from  cracks,  loose  knots  or  other  imperfections  which  may  materially 

wcakon  them.  Sometimes  they  may  havo  tips  as  snail  as  6  ins.  in  diameter,  although 
8  ins.  is  often  a  minimum  specification  limit,  with  the  butt  varying  from  12  to 

18  ins.  in  diameter.  Tho  vrriation  in  size  will  depend  to  some  -xtent  upon  the 

character  of  the  work  for  which  the  piles  are  to  bo  used.  For  permanent  work,  piles 

are  frequantljr  required  to  be  freed  from  bark. 

Eucalyptus  lias  been  much  advocated,  r.nd  used  to  a  considerable  extent 

. 

• 

in  the  Southern  and  Western  Stctes,  especially  in  marine  work,  where  it  is  com- 
paratively immune  from  the  attacks  of  narine  worinsa  It  crn  be  obtained  readily 
in  long  straight  sticks.  The  tree  is  quickly  and  cheaply  grown. 

Good  foundation  piles  ere  usually  of  white  or  Norway  pine,  yellow 
pine,  spruce  or  white  oak.  Oak  piles  rre  seldom  used,  except  in  specif  1  cases,  on 
account  of  the  extra  expense  involved.  There  is  little  choice  rs  to  pino  or  spruce 
piles.  V/honwell  selected,  oithor  material  gives  excellent  results.  In  many  places 
piles  are  kept  in  stock  afloat  so  that  they  become  thoroughly  v.r.ter-soaked  before 
being  used.  Sometimes  thoy  are  kept  in  this  condition  for  a  long  period  of  time 
-  without  being  appreciably  dame  god.  In  such  cases  however  they  may  to  some  extent 
become  alternately  wet  and  dry  by  reason  of  motion  duo  to  winds  or  currents,  rrd 
hence  thoy  should  bo  subject  to  c?reful  inspection. 

SPECIFICATIONS  FOR  TIIiBER  PILES 

Many  piles  used  for  building  foundations  in  some  cities  rrc  far  too  small 
and  their  use  should  not  be  permitted  The  "building  laws  of  tl:.o  City  of  liov;  York  in 


. 


130 

1900  permitted  the  use  of  a.  pile-  with  a  5  in.  point,  and  while-  this  may  not  be 
specially  bad  practice,  6  ins.  is  certainly  small  enough  for  an  absolute  minimum. 
The  same  building  rogut  tior.s  specified  minimum  butt  diameters  ranging  from  10  to 

ins.  depending  upon  the  pile  length.  Engineers  seldom  specify  for  less  than  a 
14  in.  butt,  although  in  building  foundations  v/hore  tho  supporting  arterial  is,  or 
ought  always  to  be,  flush  v;ith  the  top  of  tho  pile,  12  ins.  is  permissible  as  a 
minimum.  A  pile  with  a  12  in.  butt  and  6  in.  tip  is  ccttainly  small  enough  as  a 
limiting  minimum  for  satisfactory  foundation  work  for  any  building  and  nothing 
smaller  should  be  allowed.  It  is  extremely  doubtful  whether  the  smr.ll  needle-like 
piles  which  frequently  have  been  seen  driven  in  How  York  City  foundrtions  really 
add- much  to  the  supporting  power  of  the  sand  into  whicfc  they  r.ro  drivon. 
Extracts  from  tho  New  York  City  Building  Code,  1901,  Sec.  25:- 

"Pilos  intended  to  sustain  a  wall,  pier  or  post  shall  be  spaced  not  moro  than 
36  in.  or  less  than  20  in.  on  centers;  they  shall  be  driven  to  a  solid  bearing  if 
practicable  to  do  so,  and  the  number  of  such  piles  shall  bo  sufficient  to  support 
the  superstructure  proposed.  No  pile  shall b o  used  of  less  dimensions  than  5  ins. 
at  the  small  end  odd  10  ins.  at  the  butt  fpr.  short  piles,  or  piles  20  ft.  or  less 
in  length;  nor  less  than  12  ins.  at  the  butt  for  long  piles,  or  piles  moro  than 
20  ft.  in  length.  No  pile  shall  be  weighted  with  a  load  cxcee-ding  40,000  Ib. 
When  a  pile  isnot  driven  to  refusal,  its  safe  sustaining  power  shall  be  determined 
by  the  following  formula:  -  Twice  tho  weight  of  tho  hanrncr  in  tons  multiplied  by 
tho  height  of  the  fall  in  foot  divided  by  the  least  penetration  of  pile  under  the 
last  blow  in  inches  plus  one.  The  Commissioner  of  Buildings  shall  be  notified  of 
the  time  when  such  test  piles  will  be  driven,  so  that  h&  may  be  present  in  person 
or  by  representative.  The  tops  of  all  piles  shell  bo  cut  off  below  tho  lowest 
water  line.  V/hcn  required  concrete  shall  bo  rammed  down  into  the  interspaces  be- 
tween t'e  heads  of  the  piles  to  a  depth  and  thickness  of  not  less  than  12  in.  and. 
for  one  ft.  in  width  outside  of  the  piles.  Y/hore  ranging  end  cojpng  timbors  are 
laid  on  piles  for  foundations,  they  shrll  bo  of  hard  wood  not  less  than  6  ins. 
thick,  proporly  joined  together;  their  tops  lr id  below  the  Haves t  water  lino". 

'  The  San  Francisco  Law,  1910,  section  43  reads:-  "Timber  piles  shall b c 
at  1:  cist  7  ins.  in  diameter  at  tho  small  end  and  shall  be  cut  off  below  standing 
water  lire.  Titobor  piles  may  be  capped  with  concrete  at  least  ]2  ins.  thick  or 
with  timber  at  least  12  ins.  thick,  drift  bolted  to  aach  pile;  but  all  timber  shall 
be  below  standing  water  line.  There  shall  be  a  clear  distance  of  at  ]c  ast  one  ft. 
between  any  part  of  adjacent  piles.  Timber  -piles  drive-n  to  rock  or  to  refusal  may 
bo  lorded  not  to  ,oxcoed  500  Ib.  per  sq.  in  of  middle  sectional  area.  Timber  piles 
driven  in- yielding  arterial  may  be  lorded  not  to  oxcood  1  1/2  tons  per  inch  of 
diameter  of  middle  section,  but  such  piles  six  11  be  over  20  ft.  long  rnd  none  such 
shall  be  lorded  to  exceed  25  tons". 

PREPARING  PItBS 

I 

Piles  are  prepared  for  driving  by  cutting  or  sawing  the  large  ends  square 
id  bringing  the  small  ends  to  a  blunt  point  with  an  axe,  the  length  of  tho  bevel 


131 

on  the  point  being  from  1  1/2  to  2  ft.  Tho  bark  should  be  stripped  for  permanent 
work.osppcially  for  piles  below  tho  ground  surface,  and  for  piles  which  r.ro  not 
always  undor  water.  In  many  cases  the  piles  arc-  not  pointed  but  arc  driven  with 
rounded  or  square  ends.  In  softer  silty  material,  whcro  driving  is  easy,  there  is 
no  object  in  pointing  thorn,  rrid  tho  bearing  power  is  probably  greater  without  the 
points.  Blunt  piles  can  bo  driven  in  bettor  alignment,  especially  in  gravel  or 
hardpan,  as  points,  striking  obstacles  tend  to  deflect  the  piles.  Square  ends  will 
cut  or  break  through  obstructions.  Tho  upper  end  should  be  champfcred  for  a  few 
inches,  and  a  wrought  iron  band  tightly  fitted  and  driven  into  place  with  a  light 
blow.  Sometimes  the  band  is  a  little  smaller  than  tho  pile,  and  is  ham nor od  into 
it  by  a  light  blow,  either  when  the  driving  is  commenced,  or  when  the  pile  begins 
to  qD  lit  or  broom.  This  method  is  apt  to  split  off  concentric  layers  in  soft  wood 
especially  if  the  ring  is  not  placed  at  once.  Tho  rings  should  bo  made  of  tho  best 
wrought  iron,  of  carefully  welded  bands,  1/2"  to  1"  thick,  and  2"  to  4"  wide.  They 
should  bo  placed  at  the  beginning.  If  a  ring  breaks,  the  battered  portion  of  the 
pile  should  be  cut  off,  and  a  now  ring  fitted  at  once. 

An  improvement  upon  the  use  of  rings  is  the  pile  anvil  or  cap  which 

V 

carries  a  recess  of  proper  depth  on  its  underside,  and  which  the  first  blow  of  the 
hr.nnier  drives  down  upon  the  head  of  the  pile,  thus  preventing  any  injury  to  it.  The 
anvil  moves  between  the  leads  of  the  pile  driver  which  act  as  guides.  It  canies 
a  short  oak  block  on  its  top  on  which  t  he  pile  driver  hamper  falls.  By  these 

arrangements  the  head  of  the  pile  is  n  ot  only  protected  fro^.  injury  but  it  is  also 

•  ^  • 

perfectly  guided. 

DRIVING-  PILES 

The  driving  of  piles  is  a  matter  which  sjiould  receive  careful  attention  . 
A  hammer  which  is  too  light  will  accomplish  little  with  its  high  falls  except  soft- 
er ing  the  pile  head  in  crse  it  is  allowed  to  fall  directly  upon  the  latter;  and 
a  very  hervy  hammer  if  used  with  an  excessive  fall  may  easily  break  the  pile  at 
such  a  depth  that  the  failure  is  not  observed.  A  reasonably  heavy  hammer  with  a 
comparatively  sha  t  fall  and  rapid  delivery  will  produce  the  best  results.  For 


:';;,*;;//•       : 


132 

'heavy  piles  a  hammer  weighing  3600  Ibs.  with  a  foil  of  8  to  12  ft.  will  accomplish, 
all  that  is  necessary,  but  no  pile  ought  to  be  used  for  which  a  2500  Ib.  hamner 
is  too  heavy.  A  hervy  hr.araer  may  quickly  broom  the  end  of  'cn:e  pile,  end  in  order 
to  prevent  this  the  wrought  iron  ring  or  the  anvil,  already  described,  is  put  on 
at  the  beginning  of  the  operation  of  driving  and  then  pulled  off  after  the  latter 
is  completed.  Thus  both  .'/crooning  and  splitting  of  the  head  are  avoided, 

The  usual  form  of  pile  driver,  fig.  42,  consists  essentially  of  two 
horizontal  sticks  of  timber  10  ft.  to  20  ft,  or  more  in  length,  3  ft.  or  4  ft. 
apart  at  the  front  and  6  to  20  ft.  at  the  rear;  two  similar  vertical  sticks  20  to 
50  ft.  long  and  an  inclined  ladder  connecting  the  rear  ends  of  the  horizontal 
pieces  to  the  tops  of  the  verticals.  A  number  of  horizontal  platforms  are  built 
for  convenience  and  bracing,  connecting  the  inclined  ladder  with  the  verticals. 

The  hammer  is  of  cast  iron,  sliding  in  leads,  or  vertical  strips,  2"  to  3"  square, 

/ 

spiked  to   the   inside  of  the  heavy  uprights  and   faced  with  iron  straps.  An  engine 
or  other  hoisting  apparatus   is  provided  tc  raise  the  ham:rter.   In  the  commonest   form 
of  pile   dri-ver,  the  hanrner  is  permanently   fastened  to  a  wire  rope  passing  over  a 
•pulley  at' the  top  of  the  lerds  down  through  a  snatch  block  to  the  drum  of  the 
hoisting  engine. \.Co- siderable  energy  is  consumed   in  unwinding  the   drum  as  the 
hamper  falls.    In  another   form  the  rope   is  attached  to  nippers   fastened  in  a  block 
sliding  in  the   leads.   Fig.   43.   The  nippers  are  automatically  released  at  any  given 
height  by  a  'tripping  block   fastened   inside  the  leads,  allowing  the  ham.ner  to  fall 
freely,   thus   delivering  a  harder  blow  for  the   same  fall  than  with  the  previous 
form.   But  the  nipper  type  is  slower  to  operate,   the  height   of  the  fall  is  not  so 
easily  controlled;  and  there   is  danger  of  losing  the  hairier  if 'the  ground  is  very 
soft,    or  if  the  pile  springs   out   of  the   leads.   The  hoisting  engine  and  boildr  are 
mounted  on  the  pile  driver   frame  at  the  rear,    in  order  to  counterbalance  the  weighjr 
of  the  ham.ier  and  the    supported  pile. 

Pile  drivers  may  be  moved  on  firm  ground  by  wooden  rollers,    such  as  are 
used  by  house  movers.   Pile  drivers   for  railroad  work  are  mounted  complete  on   special 
cars,    the   leads  being  hinged  so    thrt  they  may  bs   lowered  to  pass  through  bridges 


133 

and  tunnels.   Of.   Eng.   tiev/s.   Vol.   48,   1902,   p.    363,    For  work   ir  water   the  entire 
outfit  is  constructed  on  a  barge,    such  as   is  described   for  ;.arl::ing  test  borings  un- 
der water,   Fig.    6,   Piles   cm  be  driven  more  economically  on  water  than  on  Irnd, 
For  driving  inclined  piles   it   is  only  necessary  to  hinge   the   le:ds  at  the   bottom 
with  heavy  bolts,   and  move   the  bottom  of  the   ladder  horizontally     to  secure  ar.y 
angle  desired.    Steam  hoisting  ermines  are  usually  used,    though  for  unir.roortc.nt 
work  or   isolated  situations,   horse  power,    or  even  ^r.n  power  may  be  substituted. 

PILE  HAMMERS. 

The  hammer  or  ram  of  the  pile  d:  iver  usua.lly  weighs  from  2000  to  5000 
Ib.   Bothlighter  aid  hecvier  v/eights  than  indicrted  by  th3s~  limits  are  occasionally 
used,  but  the  greater  bulk  of  pile  driving  is  done  by  hammers  whose  weights  are 
found b etween  these  limits.  The  fall  of  the  hammer  ranges  from  a  few  inches  to  25 
or  30  ft.  A  light  hammer  falling  through  a  comparatively  great  height  will  frequent- 
ly rebound  and  fail  to  accomplish  much  movement  of  the  pile.  A  very  hecvy  hcm.fii- 
f ailing  through  a  very  great  height.,  may  break  the  pile  or  crush  its  herd,  cc.us.ing 
a  fibrous  disintegration  called  "brooming",  Ir  order  to  prevent  this  brooming,  a 
wrought  iron  ring  or  collar,  as  previously  described,  should  be  placed  over  the 
head  of  the  pile  while  it  is  being  driven.  Generally  speaking  a  hecvy  temper  , 
falling  through  a  small  height,  will  yield  by  far  the  best  results.  For  ordinary 
engineering  work  a  haa-.er  weighing  -'rom  2500  to  4000  Ib.  felling  from  10  to  25 
ft.  will  give  excellent  results,.  Lighter  hammers  are  used  fo:.  sheet  piling.,  end 
heavier  ones  for  massive  reinforced  corcre^e  piles. 

Steam  hampers  frequently  -re  employed  for  important  -/or1:,  especially 
around  cities.  These  hammers  consist  essentially  of  a  stern  cylinder  from  2  to  5 
ft.  long,  the  piston  rod  of  which  carries  a  hervy  weight.  The  hamner  is  lowered  by 
a  rope  to  the  top  of  the  pile,  sterm  is  conveyed  to  the  piston  through  a  flexible 
tube  and  raises  the  weight  through  a  distance  equal  to  the  stroke  of  the  sn&chine, 
when  the  steam  is  automatically  cut  off  releasing  the  hammer.  The  stroke  is  much 
shorter  than  that  of  the  drop  ha— er,  but  the  >B.lows  crnbe  delivered  mud:  more 
rapidly/  While  there  isnot  much  energy  in  the  individual  blow,  on  account  of  the 


134. 

shorter  drop,   the  effectiveness   of    the  successive  blows  rry  be  r.t  least  c.s  greet, 
because  they  do  not  give  the  v.aterir.l    time   enough  to   settle  me",  compact   itself 
around  the  piles.    The  cost   of  the  apparatus   is  materially  greater  than  that  of  the 
drop  hammer. 

For  a  description  and  illustration  of  steam  ha,.r:ers  consult;    "The 
Goffer -Bern  Process   for  Piers"  by  C..E,    Fowler,   2nd  ed. ,   1905,  pp.   52-56,    figs. 
32  and  34.   ihe  principle  which  is  the  same  as  that   of  steam   forging  hammers,  was 
first  applied  by  Hasmyth  to  pile  driving  in  1845.  Modern  steam  hampers  are  nr.de   of 
different  weights:-  "In  the  cr  se   of  the  Warrington-Nasrayth  hr.ra.ner  there  r.re   three 
sizes,    550  Ib.    for  sheet  pile  work,   3800  Ibs.    for  medium  pile  work,   and  4800  Ib. 
for  use   on  heavy  work.   The  hamper  is  attached  to  the  hoist  rope  but  this  is   left 
slack  when  the  hammer   is  resting  on  t  he  head  of  the"  pile;   steam  is  turned  on  and 
the  ha..i7ier  pounds  automatically  at  the  rate  of  60  to   70  blows  per  minute  until 
the  pile    is   driven.    The  bottom  casting  which  rests  on  the  pile  is  a  bonnet  which 
3ncases  the  top  r.nd  prevents  brooming  or   splitting".   The  Crrm-hasmyth  hammer  is 
:ade   in  four   sizes;  430,   2000,   3000  and  5500  Ib .  ;   "one   of  the  peculiar  features  of 
the  Nasmyth  invention  v;as   that  of  employing  the  pile   itself  as   the   support   of  the 
sterm  hammer  parts  of  the   apparatus  while  it  was   being  driven,    so  that  the  pile 
has  the  percussive   force  of  the  deadweight  of  the   hammer   as  v*  ell   as  the   lively 
lows  to  induce   it  to  sink  into  the  ground,    One  of  the  most    ingenious  contrivances 
Df  the  pile  driver  was  the  use  of  s  terra  as  a  buffer   in  the  upper  part  of  the  cy- 
linder, which  hr.d  the   effect   of  a  recoil   spring  and  greatly  enhanced  the  effect   of 

\ 

ohe  downward  blow". 

Consult  an  interesting  report  made  at  the  j.nnual  Convention  of  the 
Association  of  Railway  Supts.    of  Bridges  and  Buildings,  Lng.  iiews,   Vol.    52,   p. 378, 
>n  the  relative  advantages  and  disadvantages  of  "steam  hammers,  or  drop  hammers   for 

ile  drivers",    for  railway  work.    See  also  Eng.  Eecord,  Vol.   63.,  April  1, 1911,  p.  369 ; 

Tineiples   of  Prr.ctice   for  Pile  Driving, 

In  En~.  Lews,   Vol.   46,   p. 282,   1901,   ilr.    S, S.Thompson  gives  a  description 
nd  illustration  of  a  Uarrington  steam  pils  driver  used   for  driving  piles   for  piers 


135. 
of  the  New  Cambridge  Bridge,  Boston,  Llass.  Some  15000  piTes  were  used  in  the  ten 

piers.  A  pile  driver  frr.me  rising  a bout  75  ft.  out  of  the  water  was  used.  The  pile 
to  be  driven  was  hoisted  and  plr.ced  ir.  position,  r.nd  the  hrmmer  allowed  to  rest  with 
its  full  weight  upon  the  pile,  thus  erasing  it  to  senile  through t he  w ater  and.  nud. 
Steam  was  then  turned  on,  the  hr.mer  pounding  r.utorn,'.tic:ll7  till  the  pile  was  driven 
to  the  required  depth.  The  weight  of  hammer  was r  bout  9800  Ib. ,  that  of  the  striking 
parts  about  5000  Ib.  It  was  a  "gravity  machine",  that  is,  the  steam  lifted  the 
piston,  then  suddenly  released  it.,  allowing  the  w eight  to  fall  'by  gravity  onto  the 
pile.  The  required  steam  pressure  was  90  to  100  Ib.  per  sq. in.  The.  hammer  was 
capable  of  giving  from  60  to  70  blows  per  minute.  In  cr  der  to  drive  the  piles  oelow 

\ 

the  surface  of  the  water  a  follower  of  white   oek,   14   ins.  square  and   fro,:  25  to 
35  ft.   long  v/as  used.   The   followers  were  capped  at  each  end  with  c  ast  iron.   The 
contractors  drove  considerably  over  100  piles   in  10  hours;   as  e.  record  days  work 
they  drove  212  piles  in  a  single   day  of  9  hours. 

SIKSIK5  PILES  BY  "/Al'^R  J3T . 

In  firm,  compact  naterial,  where   it   is  particularly  undesirable  to 
injure  the  piles  by  nervy  blows,   recourse   is  often  had  to  water  get  sinking,  This 
method  is  prrticularly  effective   in  comprct   sand,  -.-here  driving   is  vary  difficult. 
The  pipe  is  attached  to  the  sire  of  t^.e  pile  in  a  groove,   or  simply  fastened  to 
the  outside.    It   teiaiir*  ces    in  a  nos;le  ne~  r  the  point  of  the  pile,    sometimes  dis- 
charging through  an  oblique  hole  exactly  at  the  point.  Uater  is  forced  through 
under  pressure  and  removes   or  loosens  the  material  immedic-.el;;  in  front    of  tl:e  point 
V/ater  and  mud    co -B    to  the  surface  arounC.  tl.e  pile,    entirely  preventing  tl-e  skin 
friction  which  commonly  forms  the  chief  resist* nee  to4rl<vlvg.   Boulders  under 
piles  can  be  w.rried  down  by  sinking  a  pipe  to  the  bottom  of  the  boulders  and  using 
two  water  Jets.    If  the  pile  does  not  sink  by  its  own  weight,    it  .nc.y  hrve  weights 
placed  on  top,   or  the  sinking  mr.y  be   aided  by  light  blows  from  a  hr.nrcer.    If  con- 
venient, a  few  blows  should  be  given  after  stopping  the  water  jet.   'Then  the  vater 
pipe  is  removed,   the   soil  soon  packs   firmly  r.nd  the  piles  c  a- .ot  be  sorted,   even 
with  her-vy  blows,  The  soil   is   rendered  more  comprct  because   it   settles     l:en  -vet 


136. 

This  meti~vi  is  usually  employed  with  screw  piles  end.  is  the  only  method  of  sinking 
disc  piles.   It   is  ;lso  used  for  certr.in  forms  'of  reinforced  concrete  piles.    See 
^the  later  description  of  "Corrugrted  Reinforced  Concrete  Piles".  Rec:  11  the  method 
of  sinking  sheet  piles   for  the  U.  S.iTaval  Cor.ling  Str.tion,   Tiburon,  California, 
Chap,   V,   Figs.  40A,B,C. 

BS/.T-ING  POV/ER  OF  PILES. 

1.  Uhere     priven  to  a  Firm  Bottom  .    Some  piles,  pr.rticulc.rly  for  build- 
ings,    oro  driven  through       soft  ovarlying  strr.tr.  to  a  firm  material,   such  as  rock' 
or  hardpan.  These  c.re  supported  laterally  for  their  full  lengths  by  the  overlying    • 
strata.    If  not  injured  by  useless  hamraring,   their  bearing  paver   is  prr.cticr.lly 
equal  to  the  safe  crusMgg  strength  of  the   timber. 

2.  V/here  No  Bottom  is  Reached.      This   is  a  common  case  in  sv/amps  or   ' 
marshes,    or  in  loose  silt  or  quicksand.   Rr.ilrord  trestles  often  exhibit  the  "out- 
of-Sight"  pile  driving  problem.    See  ling.  Mews,   Vol.   48,  p.  442,    1902,    for  a  des- 
cription of  construction  work  on  the   Southern  Prcific  Cutoff  acres  s   the  Great  Salt 
Lake.,  Utah.   In  many  places   it  vas   found  that  mud  to  r>  d  epth  of  at   least  50  ft. 
had  accumulated.   Piles  40  to   70   ft.    long  were  driven  and  hervily  braced  for   the 
temporary  t  restles  'to    support  tveekg   for  the  train  loads  of  .material   to  b  e  dumped 
to   form  the  fills.  Kev/  Orleans   railroad    cracks   in  ir/  113:  lr?st~nces.  have  presentee,  the 
same  problem.   The  bearing  power  of  pilesin  these  materials   must  becrlculated   from 

a  c  or  si  deration  of  the  side   friction  and  the  direct  bearing  par.'  er   of  the  pile  point/- 

Let  a  =  the  cross  sectional  area  of  the  pile  at  the  point, 

p  =  the   direct  bearing  pov/er  of  the  soil   (zero  to  6000  Ib.    or  more 

per   sq  .   ft. 
s  =  the  convex   surface  area  in  sq.    ft.    of  the  pile   in  the  g  round  = 

the  average  circumference  x  the  d  epth  driven 
f  =  the   skin  friction  (100  to   600  Ib.    or  more  per  sq.    ft.) 
R  =  the   safe  load  on  the  pile  in  Ibs.   Then:- 
R  =  pa  +  f  s    ,    .    .    .......    .    .....    ..........    (1) 


Equation   (1)   gives  a  simple  formula  in  -ahich  the  constants  are  as  w 

• 

krown  as  those  of  many  of  the  formulae  in  more  common  use.  The  constrnts  usurlly  cr.n 
be  determined  in  the  field  for  the  soil  in  any  given  case,  notice  that  the  San 
Francisco  Building  Law,  1310,  Sec/  43,  is  firmed  upon  these  general  ideas  but  applie. 


137 
to  piles  driven  in  nil  c  lasses  of  materials.   Equr.tion  1  is   the  only  formula  t/hich 

can  be  applied  to  piles  sunk  by  thewrter  jet  or  driven  into   --ery  soft  soil,  v/here 

.«  ~» 

the  penetration  is   excessive.   For  s"afe  values   of  p  and  f  consult   the   figures  Givsn 
in  Chap.    2,   Patton  recommends   for  use  v.lth   equation   1:- 

f  =  100  Ib.   per  sq.ft.    for  the   softest  semifluid  sojls 

f  =  200  Ib.   per  sq.    ft.    for  compr.ct  silt  and.  clay 

f  =  300  to  500  Ib.  per  sq.    ft.    for  mixed  earths  \  ith  cons  id  er able  grit, 

f  =  400  to  600  Ib.   per  sq.ft.    for  cornp;  ct  sand  and  srnd  rr.d  gravel. 

EKAIIPIE 

Assume  a  pile  railroad  trestle   in  swamp   a  It;  p  =0,    f  =  150  Ib.'  per  sq. 
ft.  Assume  the  uniform  dead  plus   live  load  from  the  superstructure  -  6000  Ib.  per 
lineal   ft.   Select  pile  bents  .of  four  piles  e-  ch.,   bents  spr  ced  14  ft.   longitudin-y 

ally.    Er-ch  pile  carries  R  =  6000  x  14  =  21,000   Ib.   By  equation  1  the   surface 

4 
required  =  s  =  R  -  pa  =  21000=  140   sq.    ft.    If  the  pile  averages  11  in.    in  diam- 

f  150 

eter,    its  convex  surface  =  2.88  sq.    ft.   per  ft.    of  length.    Therefore  the 

penetrrticn  =  140/2.88  =  48.5  ft.   The   length  probably  would  be  specified  as  50  ft. 

If  the  piles  were  driven  into   compact  clay,    f  =  200   Ib.  per    sq.ft.; 
p  =  5000  Ib.  per  sq.    ft-,  assume  point  diameter  =  10   ins.,   then  by  equation  1 

s  =  R  -  pa     =  21000  -  5000  x  0.646J  -  91.5  tfq.    ft.    The  -penetration  required  = 

f  200 

91.5/2.88  =  31.7  ft.    Probably  the   length  would  be  spacified  as  32  or  33  ft, 

The   value   of  f  increases  as  the  pile   is  driven  deeper.    Fro -a  tects,   the 
skin  friction  may     be  assumed  300  to   500  Ib.   per  sq,    ft.    in  driving  piles  10  to 
20   ft.    into   sti*fer  materials,  and  40  to  70    ft.    into   softer  ;.irte rials.   The    skin 
friction  is   small  while   the  pile   is  being  driven,  prrticularly  if  the  blows  are 
delivered  in  rapid  succession.    It  rerches   its  nor.TK.l  .'mount  however   in  a  few 

hours  after  the  driving  has   cersed.    The  direct  berring  pov.-er   of  the  point    is 

foundations , 

/auch  greater  than  that '  f  or  ordinary  sprerd  '-*    '  T  because  the  soil  is  com- 
pacted beneath  the  pile  by  the  driving.  Experiments  shou  thrt  for  building 
foundations  in  compr.ct  material,  such  as  hard  clay  or  sand,  the  direct  be;rirg  ' 
power  of  the  point  maybe  t  rken  from  40  to  100  Ib.  per  sc.  in.  . 

3,  Usual  Pile  Formula.  In  determining  such  a  formula  for  the  bearing 
power  of  a  pile,  it  will  be  necessary  to  observe  the  oenetrrtion  ?er  blow  Curing 


I  / 

138 
the   latter  portion  of   the  period  of  driving.   The    final'  pevetrr  ticn  is   frecuentlj-. 

crlled  the  "sat"  of  the  pile.  The  energy  of  the  falling  hamrsr  or  r;  m  is  consumed 

first  by  the  per.ar.nent  crushing  or    brooming  of  the  pile,  and  second.,    in  over- 

i 

coming  the  resist,  nee  offered  to   its  motion  'ay  the  ma'cerirl   into  r/hicli  it   is 
driven.   There  rre   other  sources  of  consumption  of  energy,   sue  I:   as   tl.ie  resistance 
of  the  air,    the  resistance  of  friction  offered  by  the   lerds   of  tre  pile  driver, 
r.nd  the  resistance  of  the  lope  v/hich  is  attr-ched  to  the  hammer  in  cruder  to  re- 
cover it  r.fter  the  blow  is  delivered,   as  well  a s  one  or  tv;o   other  sources  of  the 

but 
sane  general,,  indete rrni net e  character.      For  the  reason  that  these  r.re    indeterminate 

and  do  not  form  a  very  rnaterirl  portion  of  the  actual  energy  jf  the  ramv   they 
may  be  neglected,    The  energy  ersrte:1.   in  developing  the  Actual  energ3>-  of  the 
moving  pile   is  also   neglected  b ecause   it  is  restored. before   the  pile    comes  to 
rest,,    It   is   also  supposed  that  the  pile    is  driven  under  such  ciroumstrnces  a  s  to 
accomplish  the  purpose  of  the    operation.,  end-  hence   that  no  energy  is  wasted  in 
'che  disturbance   of  the   surrounding  ..-rt:rial   or   in  useless  elastic  work  in  the 
flexure   of  the  pile   as  r.  column  by       rebounding  hammer. 

The  piles  used  for  building  foundations  are  commonly  driven  into 
comparatively  co.npr.ct  ovierirl.  An  attempt   is  rjr.de  to   judge  of  the  ultimate  or 
safe   bearing  power  of  any  given  pile  by  mersuring  the    force   of   the  blow  delivered 
and  noting  its  effect  in  producing  -penetration  on  ^he  pile.   The  amount   of  work 
V/li,  delivered  by  the  hamiier  is    equal  to   its  weight  \7  in  Ibs.   x  the  distance   it 
falls,   h  in  feet.      If  no   energy  were  wasted,    this    should  equal  the  resistance  E 
of  the  pile  :c  the  distance   s  the  pile    -.moves  under  the  blow.  Although  there  are 
a  number  of  other   frctors  these   two   terras  are  the  principal  ones   in  most  prac- 

X 

tical   formulae/  The  effective  work  delivered  by  the  hr.nner   in  ft.    Ibs.    is   equal 
to  V/h  less  p.   small  amount  consumed  by   friction  on  the  guides,   and  against  the 
air,   etc.;   but  these  losses  are  so  s.^ll  that  they  cm  be  neglected. 

If  s  =  the  penetration  or    set  of  the  pile,   then  the  mean  resistance  of 
the  -oile    during  the   movement   s  must   equal  Wh/s.    This   would  not  be   equal   to  the 
final   resistance   of  the  pile  R,   however,  bscruse   of  a   static  load  Y/li/s,  particularly 


139. 

if  aided  by  vibrations,  would  more  a  pile  when  the  s  arne  average   load  delivered 
by  the  hammer  would  not.    The  energy  of  the  hamnBr  blows  may  theoretically  be 
absorbed  in   five  different  ways:- 

1.  By  brooming  or  mashing  the  pile  either   (a)  at  the  head  of  (b)   invis 
ibly  at   the   foot,    or  somewhere  toward  the  middle;  cf.   Eng.  LTews,   Vol.   48, p. 292, 
1902, 

2.  By  bouncing,   and  striking  two  or  more   light  blows   instead  of  one 
heavy  one. 

3.  By  compressing  elastically  both  the  ~jile   r.nd  the  hammer,    and  perhaps 
the  soil. 

4y   By  overcoming  the    inertia  of  the  pile  end  the   strtic  grip  of  the 
earth. 

5.   By  useful  work  in  causing  the  pile  to  penetrrte  against  the  earth's 
resistance. 

The   consumption  of  energy  to   overcome  friction 'of  the  guides,    of   the 
air,    the  transfer  of  mechanical  energy  into  her*  are  neglected, 

la*    The  brooming  of  the  head  of  the  pile  is  a  great  source  of  loss  of 
energy,    especially  in  careless  driving..    It   should  be  prevented  or   lessened  by 
using  iron  ringe,   as   previously  described.   The  penetration     s   should  rlwrys  be 
measured  from  a  blow  struck  on  fresh  wood,    obtained  by  tr inning  or  adzing  the  top 
of  the  pile  and  after  replacing  the   iron  ring. 

Ib.    Brooming  of  t!  e   foot  of  the  pile  or  at  intermediate  points  car. 

• 

usurlly  be  detected  by  a  skillful  driver.  It  is  often  caused  by  useless  hammer- 
ing after  the  pila  has  prrctically  stopped,  or  been  driven  to  refusal.  It  always 
neans  a  disintegration  or  destruction  of  the  fibers  of  the  wood  and  a  consequent 
loss  in  bearing  power.  The  driving  should  be  stopped  before  this  occurs 

2.  Bouncing  of  the  hammer  neans   that  the  pile  has  struck  an  obstacle, 
nnd  should  not   be  driven  furthei  ,    or   else   that  the   hrm  :er   is   too -light,  or  the 
fall  too  great,   or  both.  A  heavier  hammer  or  a  shorter  drop  should   be  used  to 
secure  the   greatest  efficiency.   A  slight  bounce,  as  described  in  the   following 
paragraph  is  unavoidable, 

3.  Elastic  Compression.  At  the   instant  of  impact  both  the  pile   and  the 
hammer  will  be  elastically  compressed  but  most  of  the  energy  absorbed  will  be 
given  back  as  the  ::>ile  a  nd  the  ham/ner  move  down  in  contact/  cr.usi  ng  the  point  to 
travel  faster  than   the  herd  and  the  hamner.    If.  the  movement  is  short,   so  that 


140 
sufficient  time  is  not  allowed  for  the  pile  and  the  hamper  to  e x;r, nd  a  f ter  being 

compressed,  then  when  the  point  is  brought  to  .a  stop,  the  remnant  of  elastic 
energy  causes  a  slight  upv/ard  b  ounce.  The  amount  of  energy  absorbed  in  this  way 
is  so  small  that  it  cm  b  e  safely  neglected. 

Items  8  and  5  are  the  only  ones  which  need  be c onsidered  if  the  work  is 
-properly  done.  The  resistance  to  t  he  movement  of  the  pile  during  the  action  of 
one  blow,  will  average  Y/h/s,  but  will  not  be  constant."  Tha  resistance  will  be 
greatest  at  the  instant  the  pile  begins  to  move,  because  of  the  excess  in  the 
coefficient  of  static  friction.,  or  of  friction  at  low  velocity  over  the  friction 
at  relatively  highjelocity,  and  also  because  of  the  settling  of  the  earth  around 
and  into  irregularities  of  the  pile  since  the  last  blow,  was  delivered.  The  re- 
sistrnce  will  also  be  slightly  greater  as  the  pile  comes  to  rest,  because  of  the 
increasing  friction  at  low  velocity. 

For  the  greater  part  of  the  movement,  s,  the  resistance  will  be  approx- 
imately uniform  and  less  than  the  average  Wh/s.  This  latter  resistance  will 
represent  most  nearly  the  resistance  to  st: tic  loads,  particularly  if  vibrations 
:re  possible;  hence,  R  will  be  less  than  Y/h/s  and  might  be  represented  by  a 
fraction  of  the  form  R  =  Wh/a  +  x  . (2) 

Hence  x  is  an  amount  to  be  assumed  or  determined  by  experiment.  The 
work  diagram  for  a  pile  driven  by  a  hammer  is  approximately  of  the  form  shown 
in  Fig.  44.  The  horizontal  abscissae,  like  OD  or  JG  represent  the  total  (jnstan- 
taneous )  resistance  in  pounds.  The  total  work  \7h  delivered  by  the  hammer,  as 
absorbed  by  the  pile,  is  represented  in  the  diagram  by  the  area  ODEFGJ.  The 
•unif-orm  resistance  OB  is  the  best  measure  of  the  future  r  esista.nce  R  of  the  pile. 
It  is  required  to  determine  Me  resistance  OB,  in  terms  of  known  constants. 

Construct  the  rectangiS  OBCK  whose  area  equals  ODEFGJ  =  OBHSF  +  BDE  + 
FGH,  as  follows:  Neglect  the  work  FGH.  Consider  the  decrersing  excess  resistance 
BDE  to  the  first  inch  of  penetration,  BE  =  1  inch,  and  the  initial  excess  BD  =  3 
times  OB.  This  is  purely  an  assumption  but  it  can  be  considerably  modified  without 
greatly  affecting  the  results.  Other  assumptions,  of  the  same  nature  can  be  ma.de 


141 
with  equal  probability,   but   the   fr.ct  that   they  would  not    influence   the   final 

results  justifies   in  a  mar  sure   the   assumptions  made  r.bove.   From  fundamental 

geometric  principles  the  area  of  the   triangle  SDE  =  3D  ::  BE  =  3/2  OBo    The  rctual 

2  ~ 
area  of  the   shaded  figure  BBME  is  assumed  =  2/3  the  r.rer.   of  the  triangle  BDE,   or 

numerically  =  OB. 

To  make  the  rectangle  DECK  -  the  area  of  the  work  diagram,  make  JHDK  = 
3DME  -  OB  numerically,  or  make  JK  =  unity.  Then  the  area  OBCX  becomes  Wh  = 

B  (s  +  1)  and  H  =  V/h/s  +  1 ........ .•;'..  .."(3) 

If  h  is   in  ft.,   s   in  inches,  B  =  12  Wh/  s  +  1 .    (4) 

If  a  safety  factor  of  6  is  used,   then   the    safe  R  =  r  is:-  r  =  g  Vfo (  .5) 

8+1 

Equation  5  is  the  so-called  ''Engineering  Liews"    formula,   deduced  by 
A.M.Wellington  and  first  published  together  with  elaborate  discussions   of  fourteen 
other  formulae  in  the  Engineering  Isews,  Vol.20,  p.    511-512,   Dec. 29, 1888.  A  fuller 
discussion  and  amplification  of  the   formula   is   given  int:e  Trans.  Am.   Soc.    C,E. 
Vol.27,   pp.   99-129,   Aug.    and  hov.    1892. 

The  Eng.  .Hev/s    formula   is  critized  because  it  maJres  x  in  equation  2  a 
constant;   that  is,  unity;  v/hich  of  course   is  not  correct   for  vr.rjdng  soils  or 
weights   of  hr.ismers.   Practically  however   if  r  is   less  than  unity,   the    formula  voul^- 
give  results   for  E  greater   thrn  the  co-.ipresEive  strength  of  the    timber,   .us  a 
matter  of  fact  if  the  penetration  is  less  than  1",    say  1/2",    it  usually  means 
merely  that  the  pile   is  brooming  rnc.  that  the  point  probably  moves   little   if  rt 
all.    If  ::  is  made   greater  than  unity,   as  already  pointed   out,    it  does  not    vitally 

affect  the  results  within  reasonable  limits. 
\ 

SPECIAL  PILS  FORMULAE 

The  amounts  of  the  excesses   shown  by  BD  and  HG     in  the   figure  depend 
Almost   or   quite  entirely  on  the  character  of  the  material  into  v/hich  the  pile   is 
driven,    and   it   is   impossible  to  assign  either   exact  values   to    them  or   their 
variations,  Hor  is    it  known  whether  there   is  any  material  portion  of  the   irregular 
line  DlffiEG  which  is   exactly  parallel  to   OJ.    Indeed  the  sh-;,->e  r.nd  the    area  of  the 
figure  which  is   ecurl  to   the  hr..:-:ier  energy,  V/h,   depends   essentially  upon  the 


\ 


142 
character  of  the  material  and.   the  surface  of  the  pile,   Conse^uen^y,   it   is  quite 

impossible   to   assign  the    constant  width  OB  to  the  rectangle  which  represents  the 

\ 

hammer  energy,  and  then  call  it  the  sustaining  -capacity  of  the  pile,  The  set  s  is 

} 

a  matter   of  observation,   but  for  the  reasons  that  have  just   boen  given  x  cannot 

possibly  be  a  constant  and   it   is   impossible  to  exactly  deteraira    its  varirble 
value.    J.Foster  Crowell  writes  for  static  loads  x  =  1   +  n,   raid,   for  dynamic  or 

vibratory  loads  x  =  1   +  n  +  n'.  He  would  determine  the  value   of  n  by  observing  the 

, 
penetration  s1    in  inches  under  a  blov/  of  40,000   ft.    Ib.   delivered  to  the  pile  and 

then  make  n  =  I/2'(~at .  This  standard  fclow  would  'be  produced  by  a  2000  Ib.  hcv.-...:er 
falling  20  ft.  or  by  a  3000  To.  hammer  falling  13  1/3  ft.  He  advises  giving  n1 
various  values  dependent  upon  the  character  of  the  lord  v;bich  the  pile  is  to 
carry.  The  following  table  gives  the  values  n  and  n'  indicated  in  his  prper  on 
pile  driving.  See  Trans.  Am.  Soc.  C,E.  Vol.27,  1892,  p.  99.  It  is  intended  for 
bearing  loads  only  which  always  must  be  3e  ss  than  the  crushing  or  column  resistance 

of  the  pile.  , 

TABLE  BY  J.    FOSTER  CRO'TELI. 


s'    inches.' 

n  =fs"T 

2 

i    n'                                     Classification 
1 

i 
i 

3.125 

0.175 

0.1 

Large  bldgs.    to  contain  light  machinery  in  motion 

0.25 

0.250 

.    0.2 

Long  span  bridge  abutments   for  railv.r.ys 

1 

0.50 

0.354 

0.3 

Long  span  bridge  -abutments    for  highways 

| 

;. 

•  0.75 

0.433 

0.4 

Bldgs.    to  contain  heavy  machinery  in  motion 

:  1.00 

0.500 

0.45 

Short  span  bridge  abutments  and  railway  trestles 

;    1.25 

0.559 

0.5 

.Short  span  b  ridge  abutments  and  railway  trestles 

i 

'  1.50 

0.613 

0.55      :   Bldgs.    subject  to  extraneous  vibration 

! 

;  i.  75 

0.66S 

0.6 

Foundations   for  machinery 

3.00 

0.707 

0.7 

Elevator  towers   in  ordinary  cases     • 

{ 

<a.25 

0.750 

0,75 

Bridge    )Lers   exposed  to  current  vibrations 

< 
| 

'2.50 

0.791 

0.8 

Light  houses  exposed  to   ordinary  wave  action 

2.75 

0.830 

0.9            Foundations    for  turntables 

r 
t 

5.00 

0.866 

0.95       |  Foundations   for  pivot  bridges 

' 

5.25 

0,900 

1.00 

Chimney  stacks  exposed,  to  winds 

; 

-.50 

0.936 

' 

;  i.75 

0.965 

I 

,.00 

1.000 

Using  a  safety  f-ctor   of  6  as  before,    the  modification  of  the  mg,  Lews 

ormula,   eq .    5  becomes   for  static  loads:   R  =  2  Wh    ^.    ............    (6) 

s+l+n 
nd  for  dynamic  and  vibratory  loads,   R  =  2  V/h  ,....«.        ......    (7) 

s+l+n+n1 
In  all  the  preceding  formulae 

R  =  the  safe  sustaining  weight   of  pile   in  pounds, 


143 

W  =  weight  of  hammer   in  Ibs. 

h  =  height   of  fc.ll   ir   ft. 

s  =  mean  penetration  of  pile  in  ins.   under  the  Ir.st  blows   of  hammer. 

The   other  two  pile  formulae  which  hive   been  most  used  in  engineering 
prr.ctice  in  this  country  are   the    following: 

Sr.nder's  formula:   R  =  1,2   fTh  ,  (vfcere  f  =  1/8  to   1/3)  ,    ,    .    ,    ,    .    .    .    .    .    (8) 

s  3 

Trautwine's   formula:  R  (in  tons)   =  0.023   fUyffi  (where  f  =1_  to  1   .    .    .    .    (9) 

s   +  1  3          12 

R  (in  Ibs.)   =  52   f  \l3tfT  .    ...;........    (10) 

s   -f-  1 

In  r.ll  cases  h  is  the  height  in  ft.   of  the   fall  of  the  hammer  and.  s   is 
the  mean  penetration  in  ins.  uncer  the   last  blows.   These   and  all  other  pile   for- 
mulae  are   to  b  e  used  only  for  piles   driven  into  earth  or  similar  mrterial,   and  are 
not  to  b  e  applied  when  they  give   loads  greater  than  the   column  resistance  of  the 
pile -in  case   it   is   to  project  in  an  unsupported  manner  above  the  material  into 
which  it  is  driven,    or  when  the  results   exceed  the  crushing  strength  of  the  timber  - 
SPECIFIED  LOADS  FOE  PILES,   DETAILS,   G-ZMEH^L  BK4ARKS 

The   loads  which  may  be  imposed  safely  upon  piles  will  depend  upon  the 

) 

character  of  the  material  which  they  penetrate,   the  thorougliness  -^vith  which  they 
have  been  driven,   the   size   of  4<*ie  pile,   the  unbraced  length  of  the  pile  projecting 
above  the  material   in  which  it   is  driven,  and.  the  kind  af  timber.   Evidently  the 
permissible   lords  plrc3d  upon  piles  rlways  /.vast  be  less  than  the  crushing  strength 
of  the   timber,    and  they  can  be   specified  only  as   indicated  by  experience  in  the 
bast  practice.   TJie  building   laws   of  New  York  City  permit  a  load  of  20  tons  per 
~ypile   only,  while  those   of  Chicago  permit  or.cn  pile  to  carry  a  Icr. d  of  26  tons;   the 
ton   in  crchcrso  being  2000   Ib.      The   piles  undor  some   ftcw  York  City  buildings  arc 
probably  the   sr.irll:st   that  can  bo   found  in  structural  practice,   tho   length  iB  S'omc 
casos   being  20    ft.    or   loss,   and  the   diameter   of  th .   butt  not  more   than   10   ins. 
Pilos   of  this   character  carrying  such  loads   -re  not   allowed   in  thr;   best    engineering 
practice  although  th?y     arj  permitted  by  municiprl  regulations  under   budldings 
In  good  engineering  practice  piles   for   such  loads   would  not  be  permitted  with  butts 
less   than  12   to   14    ins.    and  with  points  not    loss   than   6  ins.    Those  srnr  11  b  uilc.ing 
Piles  w-cll  driven  to  what   is   ordii'.r.rily  termed  "refusal"  mr.j  perhaps  c-Trj''  2C   tons 


^  144 

but   they  should  not  bo  allowed   to  carry  more. 

It  should  bo  strtcd   in  this  connection  that    foundation  piles  for  build- 
ings do  not  project  r.bovo   the  .r.  tcrial  in  which  they  crodrivon  and  hone  o  they  may 
proporly  cr,rry  comparatively  high  loads.    \7nila  40,000  Ib.    is  certainly  -11  thr.t 
the  very  small  pilos  frequently  used  in  Hew  York  City  ought   to  carry.,   25  to  30  tons 
is  not   too  much  to  place  upon^  a  pile  v;ith  a  poir.t   of  6  to  0   ins.   rnc.  r   butt   of   12 
to   16   ins.   as   frequent  tosts  and  experience   have  shovn.    The  number  of  piles  rc- 
quir6d  under  any  building  cm  then  bo  determined  at  ore  c   by  dividing  the  tot.~l 
lo.-d  to  be  carried  by  the  specified  load  of  40,000  Ibs.    in  i-.-ew  York,    or  50,000   Ib, 
in  Chicago,    or  such  value  from  40,000  to   60,000  as  the    specifications   of  the   en- 
gineer may  permit,   v;hen  not  necessarily  restricted  by  municipal   lav;. 

If  piles  are  wo  11  driven  flush  with  the  surface   of  the  rnrtor'ir.l  which 
they  penetrate,   actual   test  shows  that  they  may  carry  without   settlement  as  much 
as  50  to   75  tons    (2000   lb.).    There   are  numerous   instances  in  which  loads   on  piles 
under  structures  which  do  n  ot  settle  run  from  30  to  50   tons.    If  ;nuch  unbraced 
length  of  the  pile  projects  abovj   the  material  in  which  it   is  driver.,   the   load 
which  it    is  to  carry  must  be  corrcspondigly  docror.socl.    It   is  difficult   if  not  im- 
practicable to  express  any  quantitative  relation  between  that  unbraced  length  rnd 
the  dccrerso   in  load.    There   rre  numerous   inst.-ncos   of  bridge   falsework  in  which 
loads  of  15  tons  have  been  safely  crrriec.   on  piles  projecting  20  ft.    above  the 
surface  of  the   surrounding  material,   the  piles  themselves   ranging  from  14   to   16 

ins.    in  diameter  at   the  butt.    It   is  probrbl^r  safe  practice   to   limit   the  loading  of 

/ 

r  pile   of  frir  size  and  well  driven,  which  projects   15  to  20  ft.   a'^ovo  tl.e   sur- 
rounding material,   to   15  tons  per  pilo  and  to   10  to  12  tons  when  tLe   length  of  the 
unbraced  portion  is  25  to  30   ft.    The   limitrtion  of  loads    in  &uch  cases  however 
should  bo  determined  by  the  judgment   of  the-  engineer   in  viev  of  the  circurnst-nces 
which  nry  bo   found  in  each  case.    It   can  only  be  said   in  generrl  t  or.r.s   that   if  the 
pilos  rre  in  rivers  vhc-rc  the  curr  nts  mr^  bo   strong,  more  c:  ution  .:iust  bo  exorcised 
not  to   overload  piles  with  consider,'. bio  unbraced  length  tlv  n  in  still  water. 

In  t>&  C-SG   of  v  .ildinj;   found.rtions  .    it   is  very  cs^eptirl    tl-.rt  .settlement 


145 
should  bo  reduced   to  an  absolute  hiiniraum,   and.  if  a  sr.r.ll    ~^our.t   is  unrroiclable, 

that   it  should  bo  uniform.   H,nco  when  piles  ar?  used  for  sue:?  purposes  they  should 
be  driven  to   some  hard  arc"1,  unyielding  str  -;un:  •  ':ich  i^-di"  tcly  overlies  bc.f.roc:.-; , 
or  which  has  r.  thickness  of  at   least  12    -co  15  it.    If  piles  .'re   driver  directly  to 
bodrock  they  mus  t  bo  surrounded  by  r.  ;:r.tvirir.l  sufficiertly  stiff  to  prevent  any 
lateral  motion  of  their  upper  pr.rts.   There   is  danger  in  such  conditions   of  tho  piles 
swinging  over  lr.torr.lly  or  pivoting  on  the  rigid  supports  r.t  tho  points.    It   is 
bettor  therefore  unless  tho  possibility  of  lateral  .notion  is  c  ertr.inly  r. voided,   to 
drive   into  a  stiff  .natorial  to  prr.cticrl  refusr.l  rather  tirn  to  solid  rock. 

'.'/lion  piles  r.rc   driven  t  IrrouGh  some  clnssos   of  m:.torir,l  is  v.'ill  bo 
r_cessr.ry  to    fit  to   their  points   iron  or  stool  shoes,   Cf.   Fi^s.45.   Those   shoes  ;.rc 
•isur,lly  of  hr.rd  or  chilled  cast  iron,  although  str.ps    of  \vrou j'ht  iron  bent   to  fit 
around  the  points  and  spiked  to   the  latter  hrve   &O;TD  times   been  v.soc"..    The  cast  iron 
sho.js   or  points  are  made   in  a  number   of  different  patterns.   They  r.ro  securec.  to  tho 
bluntly  dressed  ends  of  the  pilos  by  either   straps   or  a   single  contr.-.l  dov/ol.   They 
usually  woi^h  from  25  to  40  Ib.      Shoes  v/oi shins  28  to  30  Ib.   hr.vo  been  found  very 
satisfrctory  in  pile   driving  through  riprrp  -re1,   submerged   sticks   of  timber,    Fiss. 
45  A,   B,   C,   D.    exhibit   shoes   of   strap  iron;  45  2,    F,   3,   arc  oxrniples   of  cast  iron; 
consult  "Dor  Grundbau"  by  Strukcl,   Plato   12,   Figss  15-22.    Figures  45  E,    I,   J 
illustrate  recent  cast  iron  3ioos   for  piles.    The  plus  shoes,   Fijs.  45  E,I,   arc- 
attached  to  the  pile  tip  by   four  straps  as    shov.n,    spiked  to  the  pile.    They  arc 
made  of  a  variety  of   dimensions  and  vvoishts  froai  14  to  212  Ibs.   The   sheet  shoe, 
Fig.45J,    is  intended  for  coffer  dam  work  or  for  v;ide  Squared  piles  and  is  ;rdc  in 
weights   from  17  to   142  Ibs.,    sec  horvy  sheet  piling.    Fig. 38     of  theso  notes,    The 
points   of  both  plug  and  shoot   shoes,   Fig. 45  H.I,J  are  chilled  and  the  .-netrl  cast 
around  the    straps. 

Shod  piles  may  without  dif f iculty  b o  driven  through  stone   filled  crib 
v/ork  either  new  or   old  or  through  any  similar  .,r. ss   of  nrterirl  provided  trie   broken 
stones  are   not  more  than  a  bout  18  or  20  ins.    in  their  greatest  dimensions.   Pile 
foundations  have  been  successfully  constructed  for  hcrvy  retaining  and  bulkhe-d 


146 

walls   for   the    foundations  of  v/hich  it  has  been  nccess/ry  to  drivo   shod  pilos 
••;:  rough,  "stor.s   filler,  crib  v,oric  25  ft.    in  depth .' irplaco   ovor  mud  and  s  ilt  at  Icr.st 
50   ft.    in  depth  b~lov;  the  bottom  of  the  crib  vcrl:.   Indeed,   thore  have  boor,  instances 
vhere  unshod  piles  hr.vo   been  driven  through  submerged  solid  timber  platforms.    It 
•••••ill  however  be  fourd  impr:  cticr.blo  to  drive  even   shod  piles  through   masses  of 
boulders   of  cons  id  e-^able   size. 

In  driving  piles  through  groat  d  c-pths  of  soft  material,  particularly 
if  there  bo  masses  in  it  relatively  hard,    it  is  nocossrry    co   orercise  great  ore- 
caution  lest  the  points  of  the  piles  wander.   Piles  suitr.blo  to  such  conditions 
must  be  vary  lon^  r.nd  their   grcr.t  loni'ths  v.lll  prevent  t)  on  from  bcin™  very  stiff. 
The  points  r.re  therefore  easily  dofloctod  fro.n  their  proper  directions   if  t?j.c-3r  moot 
oblicuoly/a  harder  portion  of  the    .material  than  thr.t  \/hich  surrounds   it.   On  the 
other  hand,    if  piles  are  being  driven  in  very  hard  end  r'-sistant  ,:E.teri&.l,   tlere   is 
danger  of  too  hard  driving.  After  a  pile  he. s  been  brought   fir.nly  to  what   is  called 
refusal   it   is  '.verse  than  useless  to  continue  hammering  it.    The  continued  jlovvs 
of  the  hazier  v/ill  be  very  likeljr  to  brea1:  the  pile  at  a  knot  or   other  weal<:  place. 
Consult  articles   on  pile  driving,   Eng.  i>;ev/s,   B51.49,    1902,  pp.   292,   294. 
PREPAMTION  OP  PILE  !PO?S  -  CAPPING  OF  PILES 

• 

Piles  should  be  cut  off  at  a   level   belov;  the  permanent  water  line  and 
sufficiently  far  below  to  permit  any  timber  grillage  or  other  platform  to  be 
permanently  vet,    so  that  It  may  be  durable  for  an  indefinite   length  of  time.  After 
having  been  cut  off,    the  piles  are. capped  usually  by  10  31  12  in.    or  12  ::  12   i 
timbers.    The   capping  timbers  may 'preferably  be   of  yellow  pine  or  orko    In  the  T'est 
they  mcy  be  Oregon  pine,    sometimes  redwood  s  ticks  ere  used.  Eedv-ood  is  weak  relati   e- 
ly  in  strength  but  lias  the  advantage   of  high  durability  cgainst'  decay.   Hie  greet 
weight   of  timber  platforms  and   of  their  superincumbent   lords  is  usually  sufficient 
to  hold  the  capping  sticks  in  piece  upon  the  piles,   particularly  where  concrete   is 
rammed  in  the   spaces  betv/een  timbers  of  each  layer.   Sometimes  as  an  added  pre- 
caution,  the  capping  s tic":s  and  grillr    e   timbers  are  drift  bolted  to- each    other  and 
to  the  heeds   of  the  pile^o    Ck.rs  shoul  .  "je-  a::ercised  not  to  injure  t>s  pile  heeds 


147. 

The  grillage  timbers  above  the  caps  are  to   be  placed   in  one  or  tws  continuous 
layers     of  10  x  12  ins.   or  13  x  12  ins.    sticks   at  ri3ht  ar.gles  to  each  other,   as 
shown  in  Fig.24.     Each  alternate   stick  in  the  upper   layer,    if  there  are  tvo,  may 
be  omitted,  and  the  resulting  space   filled  with  concrete.    On  t!,e  top  of  this   grill- 
age is   to  be  placed  the   concrete  or  o'cher  footins  of  the   foundation  wall  of  the 

building. 

If  the  material  surrounding  the  piles  is  very  soft  it  is  sometin-.es  ad- 
visable to  excavate  it  from  2  to  4  or  6  ft.  b*10*  their  tops  and  fill  the  resulting 
space  with  concrete  solidly  rammed  in  among  and  around  the  heads  of  the  ?iL 
Should  the  material  at  the  bottom  of  this  excavated  volume  be  very  soft,  it  wi. 
be  necessary  to  fill  in  10  or  12  ins.  of  sand  or  place  a  layer  of  boards  on  which 
to  start  the  concrete  mass.  By  this  d evice  the  tops  of  the  piles  will  be  firmly 
collcred  and  held  in  their  relative  positions,  thus  adding  to  th*  general  .stiff- 
ness of  the  foundation,  as  shown  in  -Figs.  39  and  40A.  The  breat  advantage  of  cap- 
ping piles  tot*  a  layoff  coraraio  is  tet'S  it  does  not  require  the  piles  to  bo 
aligned  carefully  or  to  b  e  cut  off  at  cxrctly  the  same  level.  This  is  particularly 
true  where  the  concrete  is  reinforced  as  in  footings,  Fig. 30, 

.  Where  it  is  necessary  to  sav/  off  pile  heads,  under  water,  the  best 
results  can  be  obtained  by  a  circular  sav:  mounted  on  a  vertical  shaft  supported 
upon  a  movable  frame,  the  frame  sliding  up  and  dovn  between t he  leads  of  an  ordin- 
ary pile  driver,  Fig.46.  See  also  Fowler,  Ordinary  Foundations,  Fi:3.35,P.57.  The 
saw  is  operated  by  machinery  preferably  by  an  electric  motor,  installed  upon  the 
pile  driving  scow  or  upon  a  temporary  platform.  For  a  complete  description  of 
apparatus  similar  t'o  the  above,  see  Eng.  Hev»s,Vol.46,  1901,  P.282.  The  work  is 
sometimes  done  by  hand  with  an  "alligator"  sav,  which  consists  of  a  steel  blade 
similar  to  a  large  cross  cut  saw,  mounted  on  a  rigid  wooden  fra,e  and  swung  back  and 
forth  from  above.  In  the  best  work,  divers  occasionally  are  employed.  In  tidal  water 
great  care  must  be  exercised  if  it  is  necessary  to  have  the  tops  cut  off  at 
elevation.  The  position  of  the  piles  under  water  is  sometimes  »*k*  by  a  slight 
wooden  frame  called  a  "spider". 


:  t 


148 
Although  t>e  positions  in  which  the  piles  r.ro  to  b  a  driven  are 

specified  and  precisely  indicated  on  plans,  it  usually  is  not  possible  to  maintain 
such  accuracy  when  they  are  driven,,  The  plan  of  an  actual  foundation  when  ready 
for  capping  may  lose  all s ambiance  to  the  plan  on  paper  but  usually  it  will  not 
be  difficult  to  draw  the  pile  heads  sufficiently  into  lines  to  be  properly  capped 

c.nd  with  the  specified  number  of  piles  within  t>,s  outline  of  the  foundation. 

i 

PIgES  I  IT  SOFT    .-G-BOUMP  • 

In  alluvial  or  filled  land   or  swamps   it   is  frequently  impossible   to 
drive  piles  to  a  solid  bottom.    In  such  cases  reliance   is  placed  wholly  upon  skin 
friction.    Piles  can  sometimes  be  pulled  down  by  a  block  and  tackle,  pushed  down  , 
by  the  deadweight  of  a  hammer,    or  driven  by  a  few  very  light  blows.   Nevertheless 
after   the. mud  has  had  time  to   settle  for  24  hours  or   longer,  a  large  bearing- 
resistance  maybe  developed.   In  these  cases  serious  settlement  may  occur,  especial- 
ly if  the  super-structure   is  subject   to   shocks   or  vibrations   fro.-.i  moving  loads, 
Such  piles  are  usually  driven   from  30  to   60  ft.    or  more   into  the  soft  material 
There  are  many  sites   for  railway  and  other  structures  which  will  not  permit  a  pile 
to   be  driven  to  a  solid  bearing.   Goal  docks  have  been  built   on  the   banks   of  the 
Hudson  River  at   Hoboken,   1J,J,  ,   railway  trestles  have  been  constructed  along  the 
northern  shores  of  the  C-ulf  of  Mexico,    anc.  along  the  alluvial   banks   of  rivers,    on 
Tile  foundations  in  which  the  piles  have  reached  no  solid  stratum.    The  recent 
"ork  on  the   Lucin  Cutoff,   Salt  Lake, for   the  So. Pacific  Railro?d  has  been  mentioned 
in  an  earlier  paragraph. 

On  account   of  this  possibility  of  serious  settlement,  piles  for 

building  foundations   should  always  be  driven  to  a  firm  bearing.    If  it   is   impossible 
to  reach  firm  bearing,   very  high  or  heavy  buildings   should  be  prohibited.    If  piles 
support  a   superstructure  a  considerable  distance   above  ground,    or  if  they  are 
driven  through  very  loose  material  to  solid   rode,   there    is  denser  of  the  structure 
swinging  over  laterally  under  heavy  loads,   hence  structures  built   in  this  manner 
should  be  solidly  brrcsd  laterally.   To  give  increased  lateral   stability.,   piles    fre- 
:.itly  are  driven  on  a  b.rcter.    This  recuires  c   specirl    for/.!  of  pile   driver.    Batter 


149 
piles  are  used  principally  for  railroad  trestle  work,  where  the  outside  piles  of 

each  b  ent  are  sloped  downward  rnd  outward.  Sometimes  a  ro-,  of  Tiles  is  driven  on  a 
batter  around  the  outside  of  a  building  or  pier  founletion  to  increase  the  resist- 
ance to  lateral  stresses  which  might  arise  from  earthquakes  ox  blors  from  moving 
ships  or  drift.  This  method  was  adopted  for  the  pile  foundations  for  the  Great 
Western  Power  Company's  paver  ststion  along  the  Oakland  Estuary,  primarily  it  is 
stated  to  provide  stability  cgainst  earthquake  shocks. 

Occasionally  when  a  pile  is  driven  point  downward,  as  is  the  usual  case, 
wet  sand,  quicksand  or  saturated  silt  may  force  the  pile  out  nearly  as  fast  as  it 
is  driven.  Relief  from  this  difficulty  may  sometimes  be  found  liy  sharpening  the 
butt  end  of  the  pile  and  driving  it  with  the  point  up.  The  larger  end  of  the  pile 
is  then  in  the  sand  and  will  hold  it  in  place. 

In  the  Effort  to  reach  firm  bottom  at  great  depths  piles  are  some  tines 
spliced.  This  may  be  done  by  saving  off  the  ends  s  quare,  ua  ng  a  dowel  bolt  2  ft. 
long,  1"  to  2"  in  diameter,  driven  in  slightly  smaller  holes  an  equal  distance 
into  each  pile.  In  order  to  give  lateral  stiffness,  it  is  better  to  use,  in 
addition,  iron  straps  called  "fish  plates",  bolted  or  spiked  on  the  outside. 

It  will  seldom  be  advisable  to  drive  piles  of  proper  size  less  than 
about  2'6"  betweem  centers,  and  if  they  are  large  3'  will  be  the  limiting  minimum. 
If  they  are  too  close  together  it  may  be  difficult  to  get  them  down  to  the  desired 
penetration  without  causing  others  already  driven  about  them  to  rise. 

Reference  has  been  melde  to  the  use  of  piles  as  a  meens  to  examine  a 
foundation  site  for  t  he  purpose  of  ascertaining  its  bearing  cape  city  (  See  these 
notes,  Chap.  I  ). 


EFFECT  pi?  L 

On  The 
BEARING  POr;ER  ~CF  TIMBER  PILES. 

Study  the  report  by  L.  Wagoner  and  W.H.  Heuer,  1908,  which  describes  a 
plan  for  the  development  of  San  Francisco  Harbor,  its  comnerce  and  docks;  particular- 
ly the  articles  on  piers  and  piling.,  pp.  34-39.  Here  are  described  tests  for  pile 
bearing  capacity  made  in  New  York  City,  1902,  to  determine  the  actual  bearing  paver 


*fcte£>a 


,:,:..:  id 


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150 

of  wooden  piles  in  soil  practically  identical  in  character  to  that  along  the  San 
Francisco  water  front.  Twenty  piles  were  tested,  79  to  85  ft.  long;  14-  to  22" 
butt  diameter;  5"  to  10"  point.  Each  pile  was  driven  in  water  about  23  ft.  deep; 
the  penetration  in  mud  varying  betv/en  45  and  52  ft. 

Careful  records  were  kept,  1.  of  dspth  of  penetrctiov  into  niud  from  own 
weight;  2.  additional  penetration  due  to  weight  of  5300  Ib.  ha.nner;  3.  penetration 
due  to  each  blow  from  ha  rimer  falling  10  ft.  with  penetretionobtained  at  the  end  o' 
every  5  consecutive  blows;  4.  final  penetration  due  to  each  blow  in  the  lest  5 
blows.  Piles  were  arranged  in  three  groups  of  four  piles  eechand  one  group  of 
8  piles.  On  each  group  a  platform  was  built  loaded  gradually  with  increasing 
weights  for  27  days,  and  then  allowed  t  o  re.aain  another  27  days,  noting  subsidence 
and  conditions  of  collapse  or  other  destruction. 

On  the  20  piles  referred  to,  12  were  legged  by  bolting  end  spiking  to 
each  pile  4  pieces  of  5"  x  6"  timber  30  ft.  long;  the  lov;er  ends  of  these  timbers 
being  5  ft.  above  the  pile  point.  Four  had  bolted  to  the.n  2  pieces  5"  x  6"  and 
2  pieces  4"  x  10",  ecch  30  ft.  long.  The  remaining  4  piles  had  no  lagging. 

The  object  in  lagging  was  to  determine  if  possible  the  increased  Iced 
such  piles  would  sustain  d  ue  to  their  increased"-"  sectional  and  superficial  areas. 

Due  to  their  own  v/  eight  the  piles  penetrated  mud  3  to  15  ft., average 
11  ft.  The  hammer  caused  an  additional  average  penetration  of  7.5  ft.  At  the 
tenth  blow  the  average  penetration  of  unlagged  piles  wcs  32  ft,,  of  legged  piles 
only  17  ft.  The  unlagged  piles  reouired  an  avenge  of  16  blows  to  3  et  full  pene- 
tration of  about  49  ft.;  the  legged  piles  required  an  average  of  63.7  blov;s,  of 
10  ft.  fall,  to  obtain  about  the  same  penetration.  The  Isst  five  blows  caused  un- 
lagged  piles  to  penetrate  3  ft.  or  0.6  ft.  per  blow,  while  legged  piles  sanjfc  1.2 

* 

ft.  total,  or  an  average  of  0.24  ft.  per  blow.  The  final  tests  on  loeding  plat- 
forms showed  that  unlrgged  piles  sustained  each  a  weight  of  18.7  tons;  the  legged 
piles  supported  28  to  34.6  tons  each.  All  platforms  settled  somewhat  in  the  27  days 
ile  loaded;  the  maximum  subsidence  of  any  one  pile  being  1  -11/16", 

These  Kev/  York  experiments  incUcete  thrt  the  legged  piles  in  the  30 


151 
lowest  ft.  of  their  lengths,  presented  about  double  the  superficial  area  of 

unlagged  piles  to  frictional  resistance  and  sustained  nearly  twice  as  much  weight. 
The  cost  of  the  lagging  added  about  30  percent  to  the  cost  of  the  driven  pile  v/hile 
producing  about  double  the  bearing  capacity. 

It.  is  questionable  whether  lagged  piles  should  be  recommended,  due  to 
their  cost  and  the  uncertainly  of  securing  a  lasting  bond  between  the  pile  and 
its  lagging, 

Recently  piles,  both  wrapped  v/ith  metal  fabric  and  without  it,  have  been 
covered  with  cement  mortar  by  cement  gun.  If  in  this  way  the  cement  mortar  can  be 
made  to  permanently  adhere,  not  only  should  the  pile  be  protected  bpt  increased 
in  bearing  capacity. 

When  using  single  piles  for  piers  and  docks  and  where  additional  expense 
is  justified,  the  most  satisfactory  nethod  for  increasi  ng  bearing  capacity  and 
lateral  stiffness  is  to  use  the  so-called  cylinder  pile  described  in  later  para- 
graphs, Figs.  49  and  49A. 

See  the  .Wagoner  and  Heuer  report, page  39.  for  illustrations  of  a  proposed 
method  for  sinking  lagged  piles,  reinforced  at  their  upper  ends  by  a  protectirg 
timber  cylinder  filled  v.lth  concrete  and  reinforcement. 

SCRLV7  PILES 

Screw  piles  usually  are  lade  entirely  of  metal,  though  wooden  stems 
occasionally  may  be  used.  A  common  form  consists  essentially  of  a  hollow  iron 
shaft  3"  to  8"  in  diameter,  whitJhrmay  be  made  in  sections.  At  the  lower  end  ofthe 
shaft  are  one  or  two  turns  of  a  cast  iron  screw  blade,  similar  to  an  ?uger,  the 
blade  being  1  1/2  to  4  or  even  6  ft.  in  diameter,  weighing  frora  600  to  4000  Ib. 
The  blade  or  screw  should  be  fastened  s ecurely  to  the  s fiaf t  by  s et  screws,  pins 
or  bolts.  Screw  piles  are  sunk  by  turning  them,  usually  by  hand,  with  long  levers, 
ropes  or  a  worm  gear  working  in  a  large  toothed  wheel  fastened  to  a  shaft.  They 
may  be  driven  in  almost  any  formation,  though  herd  dry  sand  is  the  most  difficult 
to  penetrate.  Care  should  be  exercised  to  keep  the  shaft  verticr.l  and  to  prevent 
twisting  it  off.  Sinking  nay  b e  greatly  helped  by  :he  use  of  the  water  jet,  which 


152 
is  easily  operated  at  the  point  of  the  screw  blade,  water  being  supplied  through 

the  hollow  shaft  of  the  pile. 

Screw  piles  have  been  used  more  extensively  in  Europe  than  in  the  U.S» 
One  of  their  peculiarities  is  the  development  of  a  high  resistance  to  pulling,  as 
well  as  to b earing.  This  property  renders  them  especially  valuable  for  marine  work 
such  as  for  lighthouse  foundations  or  beacons.  As  no  driving  is  necessary,  they 
are  usaful  where  the  shock  from  a  pile  driver  would  be  undesirable,  a s  in  the 
bottom  of  foundations  cons'tructed  close  to  existing  heavy  structures.  They  may  be 
useful  in  certain  speci£l c sses,  because  of  the  possibility  of  sinking  them  with 
less  headroom  than  that  needed  for  ordinary  pile  drivers.  A  good  illustration  is 
their  use  for  some  foundations  in  New  York  subways  and  tunnels.  See  Patton's 
Fourdations,  pp.  497-500.  Large  screw  piles  have  been  used  to  some  extent  for 
founding  bridge  piers  in  southern  swamps. 

Fig.  47  shows  the  base  of  screw  piles  driven  by  hydraulic  screwing 
machine  into  rock  chalk.  Cf.  Eng.  Hews,  Vol.  44,  1900,  p.'  90;  Proc.  Inst.  C.E. 
of  Gt.  Britain,  Vol.139,  p.  302.  The  piles  were  screwed  into  the  hard  chalk  to 
depths  between  10  and  15  ft.  and  into  softer  chalk  15  to  36  ft.  The  piles  were 
built  of  segmentral  iron  3/4"  thick,  9"  inside  diameter,  10.5  ins;  -  diameter, 
outside  the  barrel,  and  16  1/4"  across  the  flanges.  The  lower  part  or  shank  was 
of  solid  forged  iron,  8"  diameter  with  the  end  swelled  and  turned  to  fit  the 
inside  of  the  segment  iron,  and  having  a  collar  upon  which  the  latter  rested,  the 
connections  being  made  by  throe  stoel  riv&ts.  The  lower  end  of  the  shank  was  made 
to  fit  the  socket  of  a  4  ft,  cast  steel  screw  blade  of  6  ins.  pitch  of  thread. The 
length  of  the  solid  shank  was  between  10  and  20  ft.  and  that  of  the  whole  pile 
varied  between  30  and  57  ft.  The  references  give  a  full  description  of  the  hy- 
draulic machinery  and  the  pioblems  encountered  in  sinking  the  piles. 

In  an  article  by  .T.\7.  Barber,  Proc.  Inst.  C.E.  of  &«. Britain,  Vol.  138, 
p. 344,  entitled  "Victoria  Bridge  over  the  Dee  of  Queens'farj-y,  England"  is  given  a 
description  of  screw  pile  foundations  for  the  piers  of  a  movable  bridge.  The  t.vo 
piers  are  formed  of  clusters  of  screw  piles  each  cluster  consisting  of  10-6:1  dia^ 


153  = 

solid  steel  piles   fitted  with  mushroom  screws,  3  ft.    diameter  and   screwed  to 
depths  of  about  18  ft.    into  the  river  bed,  which  is  a  fine  sane,  extending  to  a 
depth  of  probably  100  ft.    Fig.   48,   cf.   Eng.  Eews,   Vol.43»    1900, p.   46,    sha's  the 
pile   screw  to  have  dished  flangc-s  and  an  Increasing  pi  tch  irwards.  T'.e  dishing 
of  the  flange  considerably  strengthens  the  screv;  and   incr-f.ses   its  bearing  power, 
while    the  graduated  pitch  enables   it  to   enter  with  less  slip  than  usual,  and.  to 
clear  itself  better  then  the  ordinary  flat   flanje   screv:  of  regulai    ;>itch.   Ec-Cl'. 
pile  res  tested  with  30  tons  deadload  for  3  days  end   ths  greatest    settle;n3nt 
observed  was  3/8   ins. 

In  Eng.  Mews.,    Vol.50,   1903,  pp.   331-358,    is  given  a  description  of  tl:.e 
Pennsylvania  Railroad  tunnel  under  the  Hudson  Kiver,  at  tier/  York  City.   This 
reference  and  Fig.   48A  illustrate  a  hervy  screv/  pile   foundation  for  the  tube 
tunnel,    Cf.   also  Trcns.  An.   Soc.'CoL.,   Vols.    68-69,    1910. 

DISK  PIL5S 

Disk  piles  are  similar   to  s drev:  piles  but  have   flat   or  conical  disks 
instead  of  screv/  blades  at  the  bottom.   2hey  must  be  sunk  entirely  by  \vater  jet  = 
Their  uses  are  very  similar  to  those   of  s  crew  piles.    In  soils  in  which  they  ^y  be 
readily  sunk,   the3^  are   cheaper  than  screw  piles,  e.nd  equally  efficient.   The   «l:aft 
may  be  aade  of  s  ections   of   screv.-  pipe  4."   to  9"   in  diaroeter,    similar  to  hecvy  r/eter 
pipe,   or  any  convenient  odd   lengths.   If  the   sinking  is   stopped  by  obstructions  . 
such  as  stiff  clay  pockets,   it  can  usually  be   started  ar;ain  by  lifting  up  the  pile 
6"  to  1   ft.   and  dropping  it  suddenly,  keeping  the  water  jet  going  :TE  rnv/>dle,Disk 
piles  were,  extensively  and  successfully  used   for  the    foundations   of  ths  Coney 
Islcncl  Pleasure  Pier;   consult  Trans.  Am.   Soc.    C,L.  ,  Vol.    8,   pp.    227-237.    Both  screw 
and  disk  piles  are  used   for  moderate  depots,   ordinarily  from  15  to  30  ft. 

PROT3XTEI!  PILES. 

For  dock  and   trestle  work  pile   foundations  usiis.llyaie   of  short   life, 
r/herever  piles  project  above  low  tide  their  tops  are  subjected   to   severe    dec:  -in^ 
agencies  of  air  and  water.  Alternate  v;etting  ?nd  d.xying  groatl^7  shortens   t"  e 
timber's   life.   Moreover,     particularly  in  v/cr.a  ->;aters  such  piles  when  unprotected 


',15. 


154 
may  be  exposed  to  destructive  boring  by  sea  worms  (teredo  navalis  and  limnaria 

terebrans),  which  feed  on  timber. 

In  recent  years  the r e inf orced  concrete  pile  has  made  its  appearance  to 
Replace  v/ood  because  it  is  not  subject  to  the  same  destructive  agencies.  Where 
wooden  piles  are  used  they  now  frequently  are  protected  by  enclosing  envelopes 
of  metal  or  concrete,  Bhese  envelopes  reaching  only  to  cl  epths  a  f  ev;  feet  below 
low  tide,  But  in  many  locations  it  is  not  feasible  to  use  either  reinforced 
concrete  piling  or  to  protect  with  metal  or  concrete  the  exposed  tops  of  v/ood  en 
piles.  Where  timber  must  be  used  without  mechanicl  protection  it  should  be  treated 
by  chemical  means  to  toughen  it  against  decay  and  to  shield  it  as  far  a  3  possible 
from  sea  worms, 

CHEMICAL  PBESERVi-TIBES  FOB  TIMBER. 

Since  1830  the  chemical  treatment  of  timber  to  increase  its  lasting 
qualities  has  been  much  studied  by  chemists  and  engineers.  The  great  advances  in 
chemistry,  particularly  the  investigations  of  coal  and  tar  products,  have  made 
substantial  strides  possible.  The  development  of  railroads  requiring  great 
quantities  of  v.x>oden  ties  has  made  the  study  of  timber  preservation  imperative. 
It  is  for  railroad  ties  and  for  foundation  piles,  particularly  those  exposed  in 
docks  and  trestles,  that  a  study  of  chemiccl  timber  preservatives  is  demanded. 
While  there  are  many  substances  which  have  been  advertised  as  timber 
preservatives  their  are  only  four  compounds  that  deserve  particular  mention: 

1.  corrosive  sublimate  (kysnizing) 

2.  sulphate  of  copper 

3.  coal  tar  oil,  or  creosote  (creosoting) 

4.  chloride  of  zinc  ( bur netti zing) . 

Of  these  four  antissptics  creosote  is  the  most  extensively  used. 

To  apply  chemicals  to  timber,  many  schemes  of  treatment  or  processes 
have  been  advanced  and  many  have  failed  commercially.  The  differences  in  processes 
lie  chiefly  in  the  moi  e  of  injection  of  the  chemical.  We  may  mention  four  methods 
of  injection:-  1.  steeping  the  wood  for  several  days  in  the  chemical  selected;  2. 
vital  suction  of  chemicals  by  the  growing  tree;  3.  forcing  solutions  through 
freshly  cut  logs  by  hydraulic  pressure  in  the  open  air.  4.  forcing  solutions  by 


•j    >. 


155 
hydraulic  pressure  applied  in  a  closed  vessel  containing  the  wood.  The  first 

method  is  still  employed  in  kyanizing;  the  second  and  third  have  been  abandoned, 
the  fourth  gradually  modified  and  improved  is  no\:  the  most  universally  used  for 
creosoting,  Consult  Apo.  F,  the  Preservation  of  \7ood,  Jolmson's  I-Iaterials  of  Con- 
struction, ed.  1909,  p.  776,  Creosoting  is  the  best  of  all  preserve tives ,  v.hen  \vell 
c'one,  it  is  t:  e  only  method  effective  against  sea  v/orms ;  but  creosoting  is  the 
most  expensive  treatment.  In  general  practice  8  to  10  Ibs.  of  creosote  is  injected 
par  cubic  foot  of  timber,  v;here  the  timber  is  exposed  merely  to. the  v:eather.  For 
tisiber  exposed  to  tsea  v.rorms  usurlly  10  to  20  Ib.  per  cu.ft.  of  timber  is  used. 

Wood  should1,  not  be  cut  after  creosote  treatment.  Such  cutting  removes 
t:  e  outer  protection  v/hich  is  the  most  effective.  Titober  to  be  creosoted  should 
be  first  frr.med,  notched-,  etc.  The  amount  of  creosote  absorbed  depends  upon  the 
density  of  the  v.;ood.  The  greatest  effects  therefore  sre  obtained  v.ith  less  dense 
v.'oods.  Creosote  improves  cheaper  open  grained  \7oods  more  tlan  the  more  expensive 
hard  varieties,  a  fortunate  condition.  Timber  and  railway  ties  properly  creosoted 
v;ill  last  from  8  to  20  years,  piles  exposed  to  sea.v.orms  from  10  to  20  years  for 
good  work  and  hig>  quality  creosote, 

Consult  "Experiments  on  the  Strength  of  Treated  Timber1,  by  v.'.X,Katt., 
U.S.Dept.  Agriculture,  Forest  Service  Circular  39.  The  conclusions  reached,  page 
21,  are: 

1.  A  hi-gl.  degree  of  steam  is  injurious  to  wood.  The  degree  of  steaming 
v/hich  produces  harm  depends  upon  the  quality  and  seasoning1  of  the  timber,  a  Iso 
upon  the  steam  pressure  anc.  duration  of  its  application.  The  limit  of  safety  for 
loblolly  pine  is  a  bout  50  Ib.  for  4  hrs.  or  20  Ib.  for  6  hrs. 

2.  Zinc  chloride  does  not  v/eaken  v/nod  under  static  loading.  Bat  there 
ere  inflections  that  the  v/ood  becomes  brittle  under  impact. 

3.  The  -Dresence  of  creosote  itself  does  not  weaker  timber.  It  tends 
ho\veirer  to  retard  seasoning. 

C,  S.  Smith,  in  a  paper  entitled  "Preservation  of  Piling  ligcinst  ukrine 

Wood 
^Borers",  U.S.Dept.  Agr, ,  Forest  Service  Circular  128,  enumerates  different  methods 

for  orotecting  exposed  portionsof  pile,  see  pp.  3  -  11.  Ee  enumerates:-  1. external 
coatings;  2.  baric  left  or.  t:  e  pile;  5.  thin  planks  over  the  pile  surface;  4.  flat 
headed  nails  forming  c  cor.tiruout  covering,  5.  hot  paints,  tars,  asphalts. ,  etc. 


156 
applied  alone  or  with  fabrics;  6.  metallic  feheetings  of  copper  or  zinc  or 

sections  of  iron  pipe;  7.  cement  casings  with  or  without  spacing  between  the  pile 
and  casing;  8.  earthenware  pipes  with  cement  joints  encloa.  r.g  the  pile;  9.  pre- 
servative t  reatmants.  To  leave  bark  on  the  pile  is  e  protection  against  marine 
borers  as  Ions  s.e  the  bark  remains  intact;  but  bark  encoureges  the  breeding  of 
inocctc,  and.  growth  of  fungi.  It  ruickly  deteriorates  rnd  is  re^c.ily  dislodged  by 
blows.  To  be  effective  en  external  coating  must  be  absolutely  intcct,  covering 
the  whole  exposed  surfr.ee  of  the  wood.  External  mechanicd  coatings  or  she? things 
are  expensive.  They  ircres.se  the  life  of  the  -aile  only  to  the  extent  of  their  own 
life.  Metal  casings  are  costly  and  at  first  efficient  but  resdily  corrode.  Mr. 
Smith  concludes  that  denser  timbers  should  never  be  treated  chemically  for 
piling  because  of  the  difficulty  of  securing  a  satisfactory  penetration  of  -;he 
oil;  that  timbers  of  open  grain  like  loblolly  pine  are  easily  penetrated  end 
embody  all  the  characteristics  of  an  ideal  pile  timber. 

Consult  "Wood  Preservation  in  the  U,S,  ,  1909"  by  <",  F.Sherfesee,  U,S, 

"* 

Dept.  Agr,7   Forest  Service  Bulletin  78,  p.   25.    The   author  argues:-  The  average 
life   of  piles   in  the  U.S.,  untreated,    is  3  1/2  years.    He   estimates  thr.t   if  all 
the  piles  were   tree  ted  their  average   life  v.ould   be  21  1/2  years.  Assuming 
4,000,000  e::posed  piles   in  use,    the  annual  replacement   for  all  piles  untreated 
would  be   1,140,000;    for  all  piles  treated,   190,000.    Such  &  status  would  give  an 
annual  decrease  of  950,000  piles  needed,    or  cfcout   159,600,000  ffit.   board  measure- 
For  the  above   figures  he  estimates   the  average  pile   to  be  40  ft,    long  and.   to 
contain  168   ft.   board  measure.    These   figures  are  certainly  suggestive.  Assuming 
piles  untreated  to c  ost  $0.20  per  lineal  ft.,   the  srving  in  pile   timber  alone 
vould  be  0.20  x  40  x  950,000  =  $7,600,000,    In  addition  therewould  be  a  further' 
saving  of  cost   for  driving,   cost  for  altering  or  rep Ice ing  other  parts  of 
structures  rne.de  necessc.r3?  by  the  remove  1  and  replacement   of  piles,   the  cost  of 
delays  and  interruption  of  business.    Th?se  are   strong  arguments   in  fcvor   of 
reinforced  conciete  piles  wherever  'their  use   is  justifiable. 

Consult  a  discussion  upon  "Tentative  Specifications   for  Creosoted 


.   r 


•••',-',     •" 


167 
Douglas  Fir  Piling  and  Lumber   for  Use  in  Marine  Structures",  and  "Notes  en 

Creosote   Oil  Specifications",  published  in  the  Second  Annual  Progress  Report 
by  the  San  Francisco  Bay  ilarine  Piling  Survey,   January  15,1322,  pp.    58-72.    On 
page  64  is  given  the  following  proposed  specification  for  creosoto  oil:- 

"The  oil  shall  be  a  distillate  of  coal-gas  or  colce-oven  tar.   It  shall 
comply  with  the   following  requirements: - 

1.  It  shall  not  contain  more  than  3$  water, 

2.  It  shall  not  contain  more  than  0.5$  of   .latter  insoluble   in  benzol , 

3.  The  specific  gravity  of  the  oil  at  38CC  co  ipa red  with  vater  at 
15.5*C  shall  be  not   less  than  (D.045. 

4.  The  oil  shall  contain  from  5  to  10$  tar  acids. 

5.  The   oil  shell  contain  not   less  than  10$  naphthalene. 

6.  The  distillate  based  on  water-free   oil  s:.^all   be  within  the 
following  limits: 

Up  to  210*0     not  more  than  5% 

Up  to  235PC  not  moie   than  25$ 

Up  to  315°C  not   less   than  45$  nor  more   than  75$ 

Up  to  355CC  not   less  than  70$  nor  more  than  90$. 

7.  The  specific  gravityof  t:.e   fraction  between  235'C  and  315'C 
shall  be  not  less   than  1.03  at  38*0  compared  with  water  at  15.5'C 

i      The  specific  gravity  of  the   fraction  between  315"C  ai'd  355CC 
shall  be  not  less  than  1.09  at  38CC  compared  with  water  at  15.5*0. 

8.  The   residue  above  355PC  shall  have  a  float-test  of  not  more 
than  50  seconds  at  70°C. 

9.  The  oil  shs.ll  yield  not  more  than  2$  colce  residue, 

10.   The    foregoing  tests  shall  b  e  .7E.de   in  cccordance  v/ith  the 
standard  methods   of  the  American  r;ood  Preservers'  Association, v/ith  the 
exception  of  those   for  tar  colds  rud  naphthalene,   s,s  specified  in  clauses 
4  and  5,  which  shall  be  made   in  accordance  v/ith  the  methods   of  the  Amer- 
ican Railv/ay  Engineering  Association. B 

The   student   is  urged  to  'examine   recent  reports  and  transactions  of  the 
Wood  Preservers  ard  Railway  Association  just  Mentioned;   also   those  of  the 
National  Association  of  Railroad  Jj-'ie  Producers. 

PROTECTED  PILE  PLATERS 

In  San  Francisco  Bay  for  docks  and  rc.ilway  moles ,   it  h£  s  been  frequent 
practice  to  drive  piles   singly  or   in  clusters   of  2,   3  or  more,  protecting  their 
tops  £bove  the  mud  line  by  coffer  dcms   of  timber  or  metal,    filling  the  annule.r 
space  between  Ike  piles  end  coffer  den  with  concrete,   plain  or  reinforced  v/ith 
fabrics  or  rods.   Fig.  49  represents  a  typical  design  used   in  Sc.n  Francisco   for 

• 

wharves.    The  piles  take  all  of  the   losd.    In  the  case   shown  there   are   3  piles, 
sawed  off  at  different,  levels,  to  give  £.  better  bond  with  the  coffer  dsrn  con- 
crete,  After   the  piles  rre    usced,  wooden,  steve  cylinders,    ba.nded,  sre  driven  or 
v.'ater  jetted  to  propei    depths  beneath  t  he  mud  line.  The  cylinders  are  tlen  sealed 


158 

at  the  bottom,  p.-mped  out,  and  concrete  deposited.  Expanded  metals  o.r  bars  are 
introduced  as  reinforcement.  The  reinforcement  is  placed  at  a  sufficient  dis- 
tance from  the  concrete  surface  to  be  thoroughly  protected.  For  t  he  v.ork  shown 
in  Fig.  49  the  r  einforcement  was  placed  4"  from  the  outer  surface  of  the  concrete. 
In  the  course  of  time  t  he  timber  cofferdam  is  destroyed  by  t  he  Teredo  and.  by 
decay,  leaving  the  armoured  concrete  as  a  protection  to  the  piles. 

A  considerable  number  of  cylinders  of  this  type  were  sunk  in  1908  for 
the  passenger  and  freight  slip,  \7estern  Pacific  Eailroed,  Oakland  mole,  California 
Thegrecter  part  of  the  dock  rests  upon  ordinary  unarmoured  piles,  some  of  which 
wer£  creosoted.  The  cylinder  piles  v/ere  used  to  support  the  buildings  and  other 
heavy  s  tructures  for  the  freight  slip  and  its  machinery.  There  were  4  wooden 
steve  cylinders  6  ft.  outer  dicmeter,  15  cylinders  4  ft.  outer  diameter,  both 
sizes  5.6  ft.  long.  The  timber  fo£  *he  wooden  stave  cylinders  was  made  of 
Oregon  pine  sticks  4  1/4"  by  4  1/4",  sized  radially  to  4"  and  beveled  to  give 
tight  joints.  The  4  ft.  cylinders  hed  45  staves  with  bands  every  2  ft.;2  bands 
were  pieced  at  the  lower  end  or  cutting  edge  and  one  band  e.s  a  finish  at  the 
top,  at  the  elevation  at  which  the  cylinder  was  sawed  to  level. 

Obviously  this  type  of  construction  is  applicable  to  the  protection  of 
one,  two,  or  any  number  of  pileso  In  some  cases  steel  shells  have  been  used 
instead  of  wooden  ones.  The  steel  shell  has  some  advantages  in  driving,  but 
only  with  difficulty  can  it  be  c  ut  off  at  the  pjroper  elevation  at  the  top. 
Steel  shells  will  resist  the  teredo  but  eventually  would  corrode  and  rust 
away,  leaving  the  interior  concrete  to  protect  the  piles.  Therefore  this  concrete 
should  be  stiffened  with  an  embedded  envelope  of  mesh  reinforcement,  distinct 
from  the  outer  shell. 

Steel  shells  or  wooden  stave  cylinders  similar  to  the  above  may  be 
driven  or  water  jettsd  to  refusal  to  considerable  d  epths  ,  ercavated  end  then 
filled  with  concrete  reinforced  as  desired.  The  upper  portions  of  the  shell 


eventually  whether  of-  metal   or  wood  will   be  destroyed.  V/hen  such  structures 

no   ordinary  timber  piles  within  them,   as   in  Fig.  49,  we  get  the  transition  to    one 

. 


'."fl-. 


159 
to  one  form  of  reinforced  concrete  pile,  na/nely,  that  form  in  which  the 

envelope  or  form  is  driven  to  be  subsequently  filled  with  concrete  deposited  in 
place.  Within  the  last  ten  years  we  have  ssen  the  transition  carried  farther  to 
piles  molded  of  reinforced  concrete,  fthich  after  proper  aging,  are  transported 
to t  he  foundation  site  and  driven  just  like  wooden  piles. 

PROT2CT5D  CYLINDER  PI  IE 
(Howard  C. Holmes, Patent  IMP.  920061) 

This  pile  is  illustrated  by  Fig.49A.  It  was  first  used  in  San  Francisco 
for  docks  built  in  1912-13.  For  proposed  bulkheads  in  South  San  Francisco  Harbor 
Projects,  1913,  such  piles  were  recommended;  the  cylinders  projecting  10  ft. 
above  mean  low  v.ster,  extending  down  20  ft.  from  mean  low  water  to  mud  bottom, 
with  15  ft.  more  penetration  into  mud,  making  the  tctal  length  of  cylinder  45 
ft.  The  untreated  enclosed  pile  is  cut  off  at  mean  low  water  level  end  has  a 
total  length  of  60  to  70  ft. 

Around  fcach  pile  is  sunk  a  wooden  cylinder  26"  inside  diameter.  The 
cylinder  is  built  of  3"  staves  hopped  with  bands  and  otherwise  constructed  simi- 
lar to  the  larger  cylinders  already  described  in  Fig. 49.  At  the  cylinder  bottom 
is  provided  a  cutting  edge.  The  cylinder  is  driven  by  an  ordinary  pile  driver 
using  an  enlarged  cap  or  driving  heed  which  like  e  hat  or  plug  fits  '^e  toP  °f 
the  cylinder.  If  driving  is  not  easy  the  water  jet  is  employed.  A  rope  gasket 
between  the  cutting  edge  and  wooden  pile  makes  a  reasonably  water  tight  joint, 
TVhen  the  cylinder  is  fully  driven  it  is  pumped  out,  the  concrete  is  deposited 
in  the  dry  and  not  until  the  interior  has  been  inspected.  Usually  reinforcement 
similar  to  thst  of  a  building  column  is  introduced.  Such  piles  can  be  built  to 
make  a  monolithic  i  .ass  with  the  reinforced  concrete  girders,  beams  and  floor 
slabs  of  z  dock  or  bulkhead.  Or  if  the  dock  floor  is  to  be  of  timber  and 
structural  steel,  or  all  of  timber,  the  superstructure  can  in  any  case  be  firmly 
anchored.  Eventually  the  wooden  stave  cylinder  decays,  but  the  reinforced 
concrete  remains  to  protect  the  pile. 

A  70  ft.  creosotod  pile  at  San  Francisco  in  1913  cost  about  48  cents 
per  lineal  ft.  or  a  total  of  033.60.  The  driving  cost  was  $4  -  $5.  per  pile, 


160. 
making  a  total   cost   for  pile   in  place  §38.60,   or  55  cants  per  lineal  ft: 

Under   similar  conditions  the    cost   of-  an  untreated  60  ft.  pile  protected 
by  v.o  oden  cylinder  was:-  for  a  60  ft.   untreated  pile  at  15  cents  per  lineal   ft. 
$9.00;  $4.00   for  driving,  making  a  total   of  $13.   in  place.  A-  45    ft.   cylinder- 
with  concrete  reinforcement  complete  as    in   fig.49A  cost  $1.50  per  lineal   ft., 
or  $67.50  total.    The   combined  cost  then  of  pile  and  protecting  cylinder  was 

$80.50. 

In  other  words  a  60  ft.  untreated  pile  protected  by  a  cylinder  cost 

• 
about  $80.  ;  while'  a  70  ft.  creosoted  pile   t  not  otherwise  protedted  cost  $38.60, 

under  the  seme  conditions  for  San  Francisco  harbor  work.  The  cylinder  piles  then 
were  twice  as  expensive. 

But  t'e  cylinder  piles  have  about  double  the  bearing  capacity  which 
.  for  dock  work  enables  the  piles  to  carry  double  floor  loads  for  the  same  floor 
framing.   .  Their  use  might  justify  a  larger  spacing  of  cylinders  under  the  dock. 
!Dn  general  however  the  great  merit  of  protected  piles,  like  fig..49A,  is  their 
durability,  their  increased  bearing  capacity  and  their  lateral  .stiffness  against 
thrust  of  flowing  earth  or  surging  ships. 


Cluster  piles   like  Fig.  49   stand  as   types  between  wooden  pile  construction 
on   the  one  hand  and  the  he:  vier  forms   of  deep  foundations  on  the   other.   From  this 
view  point  the  coffer  dam  for  a  bridge  pier  may  be  considered  a  huge  cylinder 
of  complex  construction  to  withstand  temporary  loads  and   stresses,  within  whose 
enclosing  spcce  many  wooden  piles   or  reinforced  concrete  piles  may  be  driven; 
or  within  which  concrete  may  be  deposited  below  water  and  masonry  laic1   in  tl~e 
dry.   From  the  coffer  dam  it   is  only  another  step   to  t  he  pneumatic  pile,   to 
the  pneumatic   caisson  and  to  the  huge  piers  sunk  by  deep  well  dredging  to  the 
greatest  depths  yet  reached  by  foundrtion  science. 

ADDITION!  FJLFgiLlJCES 

1.    Pilos  and  Pile   Driving;   by  A.  L.L  Wellington.;  1833  . 

2o   ;.  treatise  on  ..lasonry  Construction,   by  1.  0,  Baker,   10th  ed.  ,    1909; 
C>£3,    ,CV     "n.    367-404, 


,. 


. 


It: 


161. 

3.  Der  Grundbau;   by  M.Strukel,   1906,  p.    Ill;  plates  12-18 

4.  A  High  Powered  Locomotive  Pile  Driver,   Carrying  its  own  Turntable; 
Eng.   Kev7s,   Vol.62,   Nov.  18, 1909,   p,    538. 

5.  Protecting  Piles  Against    the  Teredo  Havalis  on  the  Louisville  r.nd 
ueshville  R,3,  ,  by  R.ltontfork,   Tians.  #31.   Soc. C.E. Vol.31,   1394,   p.   221 

60   Concrete  Shell  Casings   for  Protecting  Wooden  Piles  -against  the 
Teredo;  Eng.  News,  Vol. 63,   Jan. 1910,  p. 30. 

7.  Supporting  Power  of  Piles,   by  E.P.G-oodrich;   Trans.   Am.   Soc.   C.E. 
Vol.48,    1902,   p. 180. 

8.  Pile  Driving  Formulas,    their  Construction  and  Factors   of  Safety; 
by  C.H.Haswell;   Trer.s.  Am.   Soc.   C.E. ,  Vol.42,   1899,  p.    267 

9.  On  the  I-Ias.nyth  Pile  Driver;  by  D.J.v.Mttemore,  Trans.  Am.   Soc.   C.E. 
Vol.12,    1883,  p.  441 

10.  Uniform  Practice   in  Pile  Driving;  by  J.F.Crowell,   Trans.  Am.   Soc. 
C.E,,  Vol.27,    1892,  p.   99;  Discussion,  pp.   129,589. 

11.  Specifications  of  Am.  Railway  Eng.   end  Maintenance  of  Way  Assoc.  ; 
Eng.  News,  Vol.51,    1904,  p.   264. 

12.  Test  Loads  of  Piles  Driven  with  a  Steam  Hammer  at  San  FrancJsco; 
Results  Compared  with  Formulas   for  Bearing  Power,  by  J.J.Y/elsh,  Eng.  fiev/s, 
Vol.52,   1904,  p.  497,503. 

13.  Pile  Foundations  for  Buildings;    International  Correspondence  School 
Structural  Engineering  Course,   Chapter  on  Heavy  Foundations, pp. 51 -63, 

14.  The  Relation  of  lion-Pressure  Process   of     Wood  Preservation  to 
Pressure  Processes,   by  V,  F,  Sherfesee,  Eng.  Sews.Uarch  4, 1909, Vol. 61, p. 230  , 

15     The  Fractional  Distillation  of  Coal-Tar  Creosote,  by  A. L. Dean  and 
E,Bateman,  U-S.Dept.  Agr. , 'Forest  Service  Circular  80. 

16.  The  Open  Tank:  Method    for  the  Treatment  of  Timbers,  by  C.G. Crawford, 
U,S,Dept.  Agr,,   Forest  Service 'Circular  101. 

17.  The  Analysis  and  Grading  of  Creosotes;   by  A.L.Dean  and  £,Bateman, 
U,S,Dept.  Agr,,   Forest  Service  Circular  112. 

18.  The  Lstiration  of  ..ioisture  in  Creosoted  v.'ood,   by  A,L.Dean,' U' S.Dept, 
Agr.,   Forest  Service  Circular  134, 

19.  The  Efficiency  and  Cost   of  Conciete   for  the  Preservation  of  Piles 
Exposed  in  Sea  Titter,   by  C>G,Korton,  ic.t.  Assoc.   Cement  Users,   paper  read  at 
Annual  Meeting,   Jan. 21-25 ; 1910. 

20.  Soft  Ground  Foundations,  Panama-Pacific  International  Exposition, 
Eng.   :.]Kews,Vol.72,    1914,   p. 250 

PROBLEMS  -  Bearing  Piles 

1.  A  R,R.  trestle   is   founded  in  a  sv.'arap  on  6  pile  bents,    spcced  12  ft. 
Assign  as  the  nax.  possible  load  on  one  bent  a  dead  load  of  900  Ib.   per  lineal 
ft.,  plus  twice   the  :&.•?..   possible  live   load   from  "Cooper's  E3P'1   loading. 
Assume  a  frictional  r  esistarc  e  of  200  Ib.   per  sq.ft.,  and  a  direct  bearing  par/ er 
of  2000  Ib,  per  sq.ft.    If  piles   crnbe  se-cured  14"   in  diameter  at  the  butt  and 
10"  at  the  point,  hoi.'  far  should  they  be  driven  below  the  surface? 

2.  A  corrugater  reinforced  concrete  pile  was   sunk  with  water  jet  in 
fine,   compact   sand.  The  pile  tet^^crBfi^fection  with  diameter   {mersurod  parallel 
to  thoooldoo')   of  16  inc.  at  the   butt  and   11   inc.   at  the  point,   tapering  uniformly 
for  its   full   length  of    36  it.    The  corrugations  were  3"  oernicircle-c  extending 

the   full  length  of  the   pile.   Compute  the  bearing  power,  accoming  frictional 
resistance   on' th;  cido  of  the  pile  at  500   Ib.   and  <fir:ct  bearing  power  at  the 
•point  at  8000  Ib.   per  sq.ft.   Soc  Fig. 56. 

3.  If  the   total  p;netration  of  a  pile  was  7.5  inches   for  the   ]a  st   5 
blows  of  a  3000  Ib.   he.rn.-nor,    falling  freely  from  a  point  18  ft.    above  the  top 
of  the  pile,  compute  the  safe   load  by  Eng.  Mows   formula,   Piles  40    ft.    long, 
average  diameter  11   ins . 


162 

4.  It   is  rocuirod  to  drive  piles  with  a  2700  lb.   hamper  till   the   safe 
bearing  power  computed  by  £713.  Sows   Formula  is  50,000  lb.   V/hat   should  be  tho 
average  penetration  during  tho   last  5  blows  if  the  average  droo  of  hanmor   is 
20  ft. 

5,  A  steam  hammer  weighing  4000  lb.    striking  55  blows  -3 or  .nin.   with  a 
stroke  of  40   ins.  drives  the   last  3   ft.   of  a  rcinforcod  concrete  pile   in  2  min. 
10  see.   Coi-iputD  the  safo  bearing  power  of  the  pile  by  Eng.Kcws   formula  using 

a  value  for  x  of  0.1  instead  of  1.0,  as  for   the  drop  hEawoy, 

6.   Compute   the  ultimate  bearing  power  of  the  pile  mentioned  in  prob.    3 
by  Rankino's   formula   (Civ.   Ens.,  pp.    602-606) 


+  4  E     S     x       -  2  ESx     ,  v;hero 
i2  i 

W  =  weight  of  ram  in  tons 

h  =  height  of  fall   in  ft. 

x  =  penetration  of  pile  per  blow  in  ft. 

P  =  greatest   load  that  the  pile  will  bcrr  in  tons 

S  =  area  of  cross   section  of  pile   in  sc. ft, 

1  =  length  of  pile   in  ft. 

E  =  modulus   of  elasticity  in  tons  per   sq.ft. 

7»    Co.7iputo  the  safe  bearing  power   of  the  pile   of  prob.   3  from  Major 
Sander's   formula  P  =  77h/8x.  I^otction  same   as   in  prob.    6. 

8.    Compute  tho  ultimate  bearing  power  of  the  pile  of  prob.   3   from 
Trautwine's  empirical   formula 


V/Y  h  . 


•P  =  52  Y/ Y  h  .  Notation  same  as  in  prob.  6. 
1  +  12x 

whi  ch 

9.  Y/hat  will  b  o  the    safe  bearing  value  of  a   timber  piloAunder   the   last 

blow  of  a  1  1/2  ton  hamper  has  a  penetration  of  3/4   in.   the  fall  of  the   hammer 
being  12  ft.? 

10.  A  pile   driven  t hrough  stiff  clay  has  a  penetration  of  2   ins.   under 
the   last  blow  of  a  haanor  weighing  1000   lb.   and   falling  through  a  distance   of 

14  ft.  V/hat  will  be -the  allowr.blo  bearing  value  of  the  pile? 

11.  The   last  5  blows   of  a  4000  lb.   hammer  falling  12' 6"  drive  a  pile 
£.  total  of  4".   With  a  factor   of  safety  of  5  what   load  may  bo   carried,   by  Eng. 
ricws,   Saunder'^bnd  Trautwine's   formulas?   If  the  pile   is    spruce,  whet  minimum 
butt  diameter   is  necessary  so  thct   the    safety  factor  shall  bo   10  against 
crushing  of'-the  head? 

12.  If  the  s  tandard  penetration  s1    of  J.Foster  Crowoll's    formula  is 
observed  to  be  3/4"  and  tho   foundation  supports  a     bridge  pier  exposed  to   slight 
vibration  from  water  currents  c.nd  trains,   determine  tho   supporting  power  of  the 
pile   of  prob,    11  by  Crowoll's   formula. 

13.  A  cylindric  coffer  dem  6  ft.    outfcido   diameter   is  drive-n  around  a 
cluster  of  3  piles   into  soft  mud.    See   fig. 49.    It  consists  of  Oregon  pine   staves 
4"  thick  with  metal  be.nds   on  the   outsir'c-  but  without  bracing  within.    If  tho 
.-.iud  acts  similar  to  hydrostatic  pressure  end  there   is   safety  against  ellipticcl 
collapse- ,   what  hoop  compression  in  lb.   per   so.    in.    is   produced  at  a  depth  of 

15  ft.    if  the    interior   is   cxcavcted  and  ua'cer  pumped  out?  Would  the  timber  be 
safo  agrinst  crushing? 


163 

CHAPTER -7 

COECBETE  AgD  REINFORCED .  COITCBETE  PILES . 
Their  Advantages  and  Disadvantages. 

The  rapid  decrease  in  tho  available  timber  supply,  combined  with  improved 
and  more  economical  methods  for  producing  Portland  cement  has  led  during  the  last 
docade  to  a  widely  incf%sed  substitution  of  concrete  for  timber  in  all  classes  of 
engineering  structures.  The  concrete  pile  represents  one  of  tho  many  used  to  which 
concrete  has  been  put  successfully  as  a  substitute  for  rood.  In  Europe, Hennobique 
cast  piles  appeared  as  early  as  1896.  The  first  patents  in  the  U.S.  v/ore  taken 
out  about  1901.  Hn  the  short  time  'since  then  concrete  piles  have  grown  rapidly 
in  favor  and  now  in  numerous  instances  are  replacing  timber  piles  for  tho  support 
of  l:.oevy  structures  in  wet  or  marshy  locations.  In  ggnoral,  concrete  piles  can  be 
used  uno.oi  all  conditions  where  timber  piles  arc  applicable.  Perhaps  the  most 
marked  advantage  of  concrete  over  timber  is  that  the  former  is  equally  durable 
i:-  wot  or  dry  soil.  Tir.bcr  piles  decay  rapidly  if  subjected  to  alternate  wot  and 
dry  conditions.  The  lowering  of  tho  ground  v.ater  l:vcl  around  pilo  foundations 
constructed  in  cities  is  a  common  result  of  the  construction  of  tunnels,  subways 
or  pipe  sewers.  '  oodcn  pil_s  :ust  be  cut  off  below  t:  c  lowest  point  to  which  the 
water  level  may  reach,  a  requirement  often  attended  with  considerable  uncertainty 
In  many  cases  tho  ground  water  level  is  so  low  that  if  wooden  piles  are  used, 
extensive  concrete  filling  must  bo  placed  above  the-  piles,  requiring  expensive 
excavations.  Concrete  piles, on  the  other  hand,  may  extend  up  to  the  superstructure 
or  ground  surface  and  cm  be  bonded  monolithicslly  to  concrete  or  reinforced 
concrete  capping,  especially  when  the  reinforcement  is  pieced  to  .rake  tho  parts 
of  the  structuic  continuous. 

The  concrete  pile  costs  more  per  lineal  ft.  than  the  timber  pile,  but  in 
many  cases  may  scv_  the  cost  of  other  items  of  construction,  such  as  excavation 
to  permanent  water  levels,  additional  depths  of  piers,  footings  or  grille. jo ,  the 

cost  of  much  sheathing,  purnpin;,',  bad:  filling.  In  such  examples  the  work  is 
•simpler,  less  in  amount,  and  maybe  done  in  a  shorter  period  of  time.  Thus,  in  tho 


•  164 

final  result   it  may  bo  cheaper  to  use   the  more  costly  concrete  vc.    the  timber 
pile.   The   ideal   location  for  a  concrete  pile  foundation  is   in  filled  areas  or 
soft  deposits  ovcrlyirg  more  substantial   strata  below  them  and  v/hcre  a  varying 
v/ater  level   is  at  considerable  distance  bolow  the  surface   of  the  ground. 

Concrete  piles  are  particularly  advantageous   for  exposed  marine  work 
because  exempt   from  the  attac'-.s   of  marine  worins  but  they  arc  not  necessarily 
immune  from  the   detrimental  effects   ofifeoashorc  moisture    conditions,    vfliere  hard 

( 

driving  has  been  necessary  in  order  to  place  timber  piles  in  position,  engineers 
have  entertained  doubts  regarding  the  final  bearing  value  of  the  pile;  that  is, 
its  real  ability  to  support  the  load  imposed  on  it,  owing  to  the  fact  that  many 
piles  driven  under  these  conditions  and  removed  later,  have  been  found  to  be  seri- 
ously damaged  by  being  telescoped  or  buckled.  Timber  piles  are  injured  more  fre- 
quently in  driving  than  is  generally  supposed,  but  comparatively  few  are  over  re- 
moved, so  that  the  integrity  of  the  foundation  is  largely  a  matter  of  conjecture. 
Concrete  piles,  if  properly  reinforced,  r.ill  stand  more  driving  than  timber  ones. 
All  evidence  would  indicate  that  they  arc  relatively  uninjured  by  hard  driving. 
Concrete  piles  can -be  raac!e  larger  and  longer  than  timber  piles;  therefore  they 
can  support  grcc.tor  loads,  They  cs.n  be  proportioned  to  carry  the  particular  loads 
which  they  are  intended  to  bear.  Each  concrete  pile  can  be  made  to  satisfy  the 
specifications.  It  is  difficult  to  select  tirnbor  so  that  every  stick  will  b  e  of 
the  proper  size  and  requisite  straightness.  The  use  of  larger  piljs  permits  heavier 
loading.  This  is  conducive  to  speed  in  foundation  construction  by  permitting 
fewer  piles.  Concrete  also  possesses  special  advantages  for  forming  heavy  mono- 
lithic water  tight  sheet  piling  in  place. 

Tho  cl-iof '.disadvantages to  tho  use  of  concrete  are  a  higher  cost  per 
pile  then  timber  and  a  grerter  difficulty  ir  driving,  owing  particularly  to  tho 
use  of  larger  sizes.  Doubts  also  have  been  expressed  as  to  tho .  porms.noncy  of  form, 
in  seme  types  molded  in  plrce,  due  to  possible  distortions  effected  while  tho 

vrcon  concrete  is  setting. 

From  the  above  arguiuant  it  ,mst  not  be  concluded  ths.t  concrete  piles  will 


165 

eventually  lately  replace  timber   ones.    Thore  arc   special   locrtions    for  v/hich 

COIL  rote   is   the   logic::.!  typo.    But   for   the  greet  ,;ass   of  pile  foundrtion  work, 
ti inter  still  will  be  employed,   for  example   for  docks,   trestles,  railway  v/ork  on 
.vsrshes;    false  work  over  vet  or  e.nd    for  light  buildings.    Timber  piles  properly 
protected  by  coatings   (including  concrete  shells)   or  chemicals,  always  v/ill  have 

their  uses. 

CLASS  FICATIOK  *•  CONCRETE  PILES. 

There  are  two  general  classes  of  concrete  or  reinforced  concrete  piles 
in  .coravion  use:-  1.  piles  which  are  molded  or  constructed  in  place   in  the   soil; 
2.  piles  vliich  are  cast  or  molded  soparrtely  and  then  driven  like  timber  piles 
after  the  concrete  has  sufficiently  hrrdc-ned.   They  may  bo  driven  \i  th  a  hammer  or 
water  jotted  into  piece.   The  second  class   is  most  usual;   of  simple  square  section, 
reinforced. 

Of  the    first  class   there  arc  a  number  of  patented  schemes.   Those  deser- 
ving special  mention  are  the  Raymond,   Simplex,  Clark  and  Abbott  piles.  Any  of 
these   for  vis  :.iay  be  either  plain  or  reinforced  concrete.   For  t  he  second  class  may 
be  enumerated  Kennobique  and  corrugated  piles ,  also  a  now  form  proposed  by  Cole. 

1.   PILES  MOLDED  IK   PUCE 

Raymond  Piles.     Raymond  piles  wore  invented  in  1901.   Fig. 50.   They  arc 
formed  by  driving  a  light  steel  conical   shell   into  the   ground.;   the   shell  is   left 
in  place  and  the  space   filled  wit!:  concrete.   There  are  two  distinct  typos: 

1.  Those  driven  with  a  namr.ior  into   firm  soil 

2.  Those   sunk  with  a  water  jet  in  looser  soil 

For   the  hammer  driven  piles,  a  patented  driving  shell   is  used,   Fig. 50, 
which  consists   of  a  hocvy  .somcvrhat  cora:>lic^tod  tapering  stool  core,    fig.50A,  fitting 
inside   a  light  shell,   Fig.50B,   so  arranged  that  when  the  pile   is  driven  the   core 
mey  be  collapsed,  withdrawn  and  used  for  the  next  pile.    The   light  steel  shell  is 
left   in  the  ground  and   is  stiff  ^nough  to  retain  the   form  of  the  hole  until    it   is 
filled  with  concrete,    Fig.SOC.   The  core  is   fitted   to  an  oak  driving  block,   Fig.50A, 
sliding  i:.   leads  and   is  driven  like  an  ordinary  timber  pile.   The   shell   or  mold 
usually  is  made   of  No. 20  rolK     steel,    in  sections  8    ft.    long,   with  an  overlap. 


•t.:-'-: 


-•    .-          :       .  ..      .     • 

*-.    ..*,-.     • 


. 


• 


166, 
Ono  of  the  advantages  of  the  system  is  that  the  shells  may  bo  formed  at  the 

site,  of  sheet  steel,  if  desired.  If  reinforcement  is  required  for  column  strength 
a  center  rod  1  1/2  ins.  in  diameter  and  3  -  3/4  in.  side  rods  symmetrically  placed 
near  the  outside  of  the  shell  are  used.  The  concrete  usually  is  a  1-2-4  mixture 
thoroughly  rammc c". .  The  piles  are  :.iade  in  lengths  from  20  to  40  ft.  ,  top  diameters 
18  and  20  ins. ,  point  diameters  6  and  8  ins.  The  conical  form  aids  in  compressing 
the  soil;  it  is  claimed  to  give  a  greater  bearing  paver,  '.".lion  the  piles  are  driven 
to  bedrock  a  special  core  13  ins.'  in  -diameter  at  the  bottom  and  20  ins.  at  the 
top  is  used.   Twenty  ft.  pile  lengths  are  recommended  for  ordinary  soils  because 
t'-joir  taper  is  greater  and  the  bearing  pov;er  per  ft.  of  length  is  assumed  to  be 
STGcter  than  for  longer  piles. 

The  second  form  of  Raymond  pile,  Fig.  SOD,  is  adapted  for  use  in  sand, 
quicksand,  silt,  or  soft  earth,  easily  loosened  v/ith  a  \vatorjot.   The  shell  is 
.•iade  in  8  ft.  sections,  nost<ad,\vith  rings  on  the  upper  outside  and  lover  inside, 
of  each  section.  Each  section  as  it  sinks  drav/s  the  next  section  after  it.  A  cast 
iron  shoo  is  used  vith  a  3/4  inch  nozzle  at  the  point.  A  2  1/2  in.  pipe  connected 
vith  the  nozzle  is  held  in  place  in  the  axis  of  the  pile  by  spreaders  at  each 
joi./c.  Each  section  as  it  sinks  is  filled  v.ith-.v  ell  rammed  concrete.  The  2  1/2 
in.  pipe  is  left  in  plac.,  other  r  oinforcemcnt  is  added  v;Iicn  needed. 

Tho  groat  advantage  claimed  for  the  Raymond  pile  is  that  a  form  for 
every  pile  insures  the  corr:ct  shape,  prevents  the  washing  out  of  cement  in  quick- 
sand or  saturated  soil,  and  prevents  the  distortion  of  t he  cross  section  or  diam- 
eter by  unequal  earth  pressure  on  ^een  concrete.  The  promoters  claim  an  increased 
-bearing  pov/er  on  account  ::f  the  conical  shape;  the  advantage  is  borne  out  by 
theoretical  analysis,  assuming  homogeneous  soil  throughout  the  length  of  the 

pile,  but  in  the  case  most  often  met  in  practice  the  point  of  the  pile  is  driven 

comparatively 
into  <  firm  sub-strata  vhile  the  pile  is  surrounded  by  loose  material 

at  the  butt.  In  such  cases,  obviously,  a  pile  of  uniform  or  increasing  diameter 
dov/nv;ard  vould  be  ^referable. 


167 

SIIJPLEX  PILES 

The  Simplex  system,   Fig. 51,   consists  in  driving  to  a   firm  bearing  a 

from 
heavy,  metal  form,   Fig.51A,  with  a  hollow  circular   cross  section,  uniform  top  to 

bottom.   Concrete   then  is   introduced  and   the  form  v.i  thdrawn  in  stages  while  the 
concrete   is  rammed.  The   concrete   fills  the    space  previously  occupied  by  the   form. 
On  account   of  the  ramming,    its  section  usually  is   larger  than  that  of  the    form, 
the  liquid  concrete  being   forced  outv/ard  into  the   irregularities  of  the   soil. An 
"alligator"  driving  point,   Fig.51A,  which  closes  while  driving  and  opens  when  the 
form   is  pulled,  allows  the  concrete   to   be   forced  out   into   the  soil;  when  the  re- 
quired depth  is    reached  enough  concrete   is  lowered  in  a  special  bucket,   Fig. 51B, 
of  capacity  to  fill  3  ft.    of  the    form.   The   shell   is  then  pulled  upward  2  ft., the 
concrete  rammed  with  a  heavy  drop  hammer,    and  the  operation  repeated.    One   of  the 
ordinary  forms   of  heavy  pile  driver   is  used,    but  must  be   fitted  with  a  powerful 
hoisting  tacfele,   as    forces  as  high  as   100  tons  have  been  required  to  pull  the 
shell.    For  working  under  water,   Fig.510,  a  second  thin  shell  is   sunk  into  the  mud 
outside  of  the  driving   form,  which  subsequently  rets  as  a  form  for   that  portion 
of  the  concrete  pile  extending   through  t  he  water.  \Vhen  the    surrounding  material 
is  quicksand  or  saturated    soil,   which   tends  to   fill   the   void  formed  oy  the  driving 
shell,   a  second  light  shell  of  ho.    20  or  22  sheet  steel  may  be  slipped   inside 
the  driving  form  before    filling  and  left  as   a  permanent   fore  for   the   concrete. 

In  place  of  the  "alligator"  point,   a  cast  concrete  point  2  or  5   ft.    long,    or  a 

* 

cast  iron  or  steel  projectile  shaped  point  is  frequently  used  and  left  in  place. 

Simplex  piles  may  be  reinforced  with  vertical  rods,  Fig.51C,  but  more  frequently 
they  are  stiffened  with  interior  cylinders  of  expanded  metal  or  wire  cloth.  There 
is  apparently  no  limit  to  the  dength,  as  driving  pipe  may  Ira  added  in  sections 
.nd  the  forms  driven  through  much  harder  soils  than  is  possible  for  wooden  piles, 
'he  principal  advantage  claimed  is  increased  carrying  power  due  to  the  side  friction 
eveloped  in  ramming  the  concrete,  and  to  a  full  or  increased  diameter,  giving 
.arge  bearing  -.power  nea.r  the  bottom  and  at  the  point.  The  heevy  rr.mming  expands 
"  e  concrete  into  the  surrounding  earth,  firmly  compacting  it  and  cementing  the 


.-•   '  V. 


168 
the  pile  to  the  adjacent  sand  or  gravel.  Tje  piles  as  actually  constructed  are 

apt  to  be  so  mevhat  irregular  in  cross  section.  If  constructed  in  soil  v.hich  is 
not  homogeneous,  the  irregular  pressure  on  the  green  concrete  may  seriously  injure 
the  piles  by  deforcing  and  decreasing  the  cross  section  in  a  v/ay  which  isfsxtremely 
difficult  to  detect.  See  Eng.  News,  Vol. 69,  p. 416. 

CLARX  PILES. 

For  the  Clark  pile  the  process  consists  essentially  of  an  open-ended 
cylinder    nade   in  convenient  sections   and  driven  to  the  desired  depth.    It  is 
fitted  v/ith  inside  couplings  to  diminish  the  driving  friction.   It  usually  is 
driven  v.lth  a   sterm  ha.rner,    freruently  assisted  by  a  v/aterjet.  A  v/aterjet  is 
alv.sys  used  to  wash  the   inside  of  the  cylinder  clean.   When  a  satisfactory  depth 
is  resched  by  charging  the  v/aterjet  velves,  cement  grout   is  injected  at  the  bot- 
tom of  the   cylinder  and  fills   it  by  displacing  the   lighter  v/ater.  The  cement 
grout  spreads  out   to  some  extent  at   the  bottom,   giving  an  increased  bearing  area, 
Rods  may  be  used   for  reinforcement.   Cf.   Concrete  and  Reinforced  Concrete,   by 
K, A. Reid,   Bd.1907,   p.    442. 

ABBOTT  PILES,    Fig. 52. 

This  employe     a  novel  method  of  constructing  concrete  piles,  to£  v.hich 
additional  stmngth  and  stability  are  obtained  by  producing  an  enlarged   foot   or 
base  at  the  lov;er  end  of   the  ^ile.    It   is  a  cast-in-place  pile,   somev/hat   like  the 
Simplex,   tl^e  apparatus  necessrry  fo    form  the  pile  consisting  of  a  casing  and  a 
core.   The  casing  is  a   steel  pipe,   Figc.    52A,   B,   16  ins.    in  diameter,   3/8   in. 
thick.   The  core   is  a  smaller  and   longer  pipe,  v/ith  a  cast  steel  point  and  an 
enlarged  cast  steel  head.    The   core   fits   inside  the  caning, -its   enlarged  head  en- 
gaging the  top  of   the  casing,    itt   lover  end  projecting  some  4   or  5  ft.   below  the 
lov/er  end.    In  the  head  of  the  core  there   is  an  oak  driving  block  which  receives 
the  blovo  of  the  hammer.    The  core  is    fitted  into  the  casing  and  both  are  driven 
in  the   ground  to  the    de:,irecl  depth,    an   indicated   in  Fig.52A. 

The  core  is   then  pulled  out  and  a  charge   of  concrete   is  dropped  to  the 
•ottom  of  the    casing,  as   in  Fig.52B,   The  core    (or  rammer,  as   it  nov.-  becomes)    is 


'-•I 


.-.t  •••. 


169 
lov/ered  into  the  casing  and  d  riven  through  this  charge  of  concrete,  pushing  it 

to  either  side,  as  shown  in  Fig .520.  This  operation  of  placing  charges  of  concrete 
and  ramming  them  is  continued  until  a  large  bulb  or  foot  of  the  desired  size  io 
formed,  fig. 52D.  If  the  coil  just  below  the  foot  is  somev/hat  harder  than  above  it 
the  foot  may  flatten  out  on  the  bottom  to  some  extent.  After  the  foot  has  been 
formed,  the  casing  is  filled  to  the  top  v/ith  wet  concrete  and  then  pulled  out, 
leaving  a  concrete  column  16  ins.  in  diameter,  resting  on  a  spread  base  or  ped- 
estal,- This  column  may  be  reinforced  with  steel  rods  if  greater  strength  is 
desired  in  that  part  of  the  pile. 

It  is  evident  that  this  pile  v.'ill  carry  a  considerably  greater  load 
under  given  conditions  than  a  straight  pile  without  the  foot.  It  has  all  the 
frictional  area  along  the  stem  that  the  straight  pile  hac,  and  also  some  around 
the  circumference  of  the  foot.  In  addition  to  this  friction,  it  has  the  bearing 
value  of  the  projected  area  of  the  foot  on  the  firm  soil  at  the  lov;er  end  of  the 
pile.  This  soil  has  been  compressed  and  compacted  by  the  r aiming  of  the  concrete 
during  the  formation  of  the  foot,  and  therefore  is  capable  of  bearing  a  greater 
load  than  it  \vae  before  the  driving  of  the  pile.  Experiments  have  been  cade  with 
this  pile  in  a  number  of  different  kinds  of  soil,  and  it  has  been  found  that  the 
shape  taken  by  the  foot  is,  in  all  caces,  roughly  spherical,  Fi£.52D.  Of.  a  dis- 
cussion by  E, Abbott,  Trans.  A.r,.  Soc.  C,E,  ,  Vol.65,  1909,  p.  507. 

Many  engineers  have  constructed  concrete  piles,  disregarding  the  numer- 
ous patents,  merely  sinking  sheet  iron  casing  by  ordinary  well  drilling  methods ., 
filling  the  casing  -with  veil  rammed  concrete,  reinforced  as  desired.  Special 
champ  ferine;  ms.cl-.ine8.  fittec?.  v/ith  a  toggle  arrangement  have  been  used  in  moderately 
firm  soil  to  /ne.lre  an  enlarged  space  at  the  foot  of  a  pile,  which  can  be  immediately 
"illed  v/ith  concrete.  Cf.  Ta  lor  &  Thompson,  Fig. 208,  p. 653,  ec1...  1909.  This  gives 
:.  footing  of  roughly  spherical  she.pe,  similar  to  that  described  for  the  Abbott 
.iile.  Such  e.  footing  con  b  e  re.r.dily  made  from  2  1/2  to  "6  ft.  in  diameter. 


170 
2.  PILES  liOLDED  AMD  THEN  DRIVER. 

Most  engineers  nor;  prefer  to  use  concrete  piles  v/hich  are  molded  separate- 
ly and  then  driven,  like  timber  piles.  Made-in-place  piles  are  liable  to  serious 
defects  caused  by  percolating  water  or  unequal  coil  pressure,  defects  which  it  is 
impossible  to  detect.  Piles  v/hich  are  molded,  allowed  to  harden,  then  driven, can 
be  inspected  and  their  quality  accurately  determined,  as  little  injury  is  liable 
to  result  from  even  the  hardest  driving.  There  are  many  patented  varieties  of  the 
molded  type,  differing  from  erch  other  in  shape,  cross  section  and  method  of  re- 
inforcement. All  molded  piles  are  reinforced  v;ith  iron  or  steel  to  stand,  the 
rough  handling  to  which  they  are  subjected  in  transportation  from  the  molding  yard 
to  the  site  and  while  they  a  re  being  placed  in  the  leads  and  driven.  The  driving 
strains  are  very  great.  It  is  thought  fcy  many  that  a  pile  v.lth  reinforcement  should 
not  be  subjected  to  the  impact  of  a  hammer.  Mcny  piles  have  been  driven,  hovever 
subsequently  pulled  and  red- iven,  without  showing  any  injurious  effect.  Driving 
caps  are  constructed  with  a  hard  wood  driving  heed  and  a  cushion  of  hemp,  sand, 
sawdust  or  rubber.  Cf.  Fig. 53.  Heavy  hammers  should  be  used  in  driving.  For  the 
best  results  the  hammer  should  weigh  1  1/2  to  2  times  asmuch  as  the  pile.  Steam 
hammers  weighing  5000  Ib.  or  more  ere  chiefly  used.  V/here  soil  c  ondit ions  are 
favorable,  water  £ets  are  helpful,  either  alone  or  in  combination  with  driving. 

The  earliest  forms  of  molded  piles  are  all  of  rectilinear  cross  sections 
such  as  tire  square,  rectangle  or  triangle,  because  of  the  greater  simplicity  of 
the  forms.  Piles  may  be  cast  either  horizontally  or  vertically,  though  the  latter 
gives  the  better  results.  If  piles  are  erst  vertically  they  are  better  able  to 
resist  t:~e  shocks  of  driving  and  possess  a  higher  compressive  strength,  b  ecause 
the  layers  of  concrete  are  normal  to  the  stress,  If  the  forms  are  built  complete 
for  a  long  pile  molded  vertically,  it  is  difficult  to  ram  the  concrete  into  tl:e 
narrow  space.  To  overcome  this  difficulty,  the  forms  may  be  built  in  sections  as 
the  concrete  is  laid,  or  three  sides  of  a  rectangular  form  may  be  built  complete 
and  the  fourth  side  added  as  the  concrete  is  poured.  Piles  now  are  rr.rely  ccst 
in  the  vertical  position.  It  is  possible  to  effect  considerable  saving  in  forms 


C'JC. 


171 
by  using  the  horizontal  system  of  pouring,  as  the  upper  portion  or  lid  of  the 

form  for  square  or  polygonal  cross  sections  can  be  omitted,  entirely,  v/hile  the 
side  pieces  can  be  removed  after  24  hours  and  used  again.  Hollow  speces  frequently 
are  left  in  cast  piles  in  order  to  lighttm  them  ^7itho^t  greatly  decreasing  their 

strength. 

HEMBBIQUL  PILES 

Hennebique  piles  introduced  in  1896  were  the  first  reinforced  concrete 
piles  Gf.Eng.  News,  Vol.51,  1904,  p,233.  They  are  usually  square  in  section  with 
verticrl  rods.  The  rods  are  wired  together  near  the  corners.  Sometimes  additional 
rods  are  used  at  the  middle  of  the  sides.  See  Fig.54A.  The  lower  end  of  the  pile 
is  protected  with  a  pyrenidal  cast  iron  shoe.  The  reinforcing  rods  are  bent  to- 
gether at  the  point,  welded  and  fastened  to  the  metal  shoe.  The  piles  frequently 
are  iiE.de  hollow,  sometimes  with  a  jet  pipe  imbedded  in  the  middle  and  left  in 
place  as  additional  reinforcement.  Provision  for  jetting  .nay  be  made  in  the  lower 
end  by  the  insertion  of  a  piece  of  wrought  iron  pipe  about  3  ft.  long,  bent  in 
such  a  manner  as  to  extend  from  ths  center  of  tl'e  point  to  the  outside  of  the  pile 
just  above  the  shoe, whore  an  outside  connection  can  b  e  rncde,  and  later  removed, 
saving  a  considerable  length  of  pipe.  Hennebique  piles  occasionally  have  been 
.-.ic.de  of  triangular  cross  section  v.lth  three  verticrl  reinforcing  rods.  Fig-54B. 

CORRUGATED  PILES 

The  corrugated  pile  is  usually  octagonal  in  cross  section,  Fig. 56, 
is  tapering  in  shape,  16  ins.  in  diameter  sit  the  butt  and  11  ins*  at  the  tip. 
Each  of  the  faces  of  tl  e  octagon  contains  a  semicircular  longitudinal  corrugation 
2  1/2  to  3  ins.  in  diameter,  running  for  almost  the  entire  length.  The  pile  is 
hollow,  r/ith  a  core  4  ins.  in  diameter  at  the  top,  2  ins.  at  the  bottom,  which  is  : 
used  for  jetting  purposes.  The  core  is  made  by  the  use  of  a  tapering,  collapsible 
mold,  thus  obtaining  an  opening  for  the  water  jet  at  small  expense.  After  the  pile 
:.r s  been  placed,  this  opening  can  be  filled  with  fine  concrete  or  cement  mortar 
t:..us  Baking  e  solid  pile.  The  piles  are  molded  horizontally,  the  forms  being 
striroed  sfter  24  to  48  hours,  The  piles  arc-  kept  wet  for  et  least  ten  days  before 


. 


- 


1  7° 

J  I  r^ 

driving.  They  are  reinforced  throughout  with  Clinton  welded  wire  fabric.  The 
piles  may  be  sunk  under  favorable  conditions  by  the  water  jet  alone.  It  is  common 
however  to  employ  a  heavy  steam  hammer  striking  with  a  light  fell  on  a  special 
cushion  cap,  used  either  simultaneously  with  a  water  jet  or  at  3e  ast  to  secuie  a 
final  firm  bearing.  For  an  illustration,  cf.  Reid,  Concrete  end  Reinforced  Con- 
crete, ec"..  1907,  p.  453o  It  is  claimed  for  this  pile  that  as  the  corrugations  in- 
crease its  convex  area,  its  bearing  capacity  is  correspondihgly  increased,  on 
account  of  the  grester  surface  exposed  for  frictional  resistance.   The  corrugations 
also  r.ssict  -naterially  in  the  escape  of  water,  making  it  easier  to  jet  the  pile 

into  position. 

COLE  PILE,  Fifi*  54C 

Another  type, circular  in  cross  section,  is  formed  in  an  entirely  dif- 
ferent manner.,  in  that  it  is  not  molded  or  cast  but  is  rolled  mechanically  into 
shape.  Cf.  an  article  by  H.J.Cole,  Trans.  Am.  Soc.  C,E. ,  Vol.65,  p. 482,  A  sheet 
of  ordinary'  wire  fabric,  to-  16  gauge,  1/2  inch  mesh,  of  the  length  required  to 
make  the  pile,  is  attached  to  the  rod  which  s  erves  as  the  winding  core  and  later 
as  a  part  of  tha  r  einforcement  of  the  pile.  JThe  other  edge  of  the  sheet  is 
c.ttached  to  a  movable  platform  v/hich  is  pulled  tov;rrd  the  core  as  it  is  wound  up 
On  this  sheet  is  placed  the  other  reinforcement ;  and  the  whole  is  covered  with 
e  li.ysr  of  fine  concrete.  The  .TES  is  then  v.ound  up  like  r  jelly  roll,  fastened 
with  vire  ties  ever-/  6  inches,  end  <nore  frequently  where  needed.  In  some  of  the 
later  oiles,  the  method  of  fastening  the  outer  edge  of  the  wire  cloth  lias  been 
changed  by  omitting  the  wire  ties  and  substituting  a  rivet  with  its  end  upset  so 
"•>at  it  is  slightly  larger  in  diameter  then  the  mesh  of  the  cloth.  These  rivets 
are  inserted  in  the  outer  ed^-e  of  blie  cloth  with  this  upset  end  upward,  and  as  the 
pile  is  rolled  up,  t?iey  are  forced  into  the  raeshes  of  the  fabric  in  the  body  of 
v-e  pile,  thus  tying  or  rather  buttoning  it  together.  The  platform  on  which  the 
pile  is  ,'uoi"1  ed  is  incline:"!  so  that,  without  any  lifting,  the  completed  pile  is 
rolled  therefrom  to  thG  car,  v.;hic;i  is?  to  carry  it  to  the  seasoning  yard.  The  plat- 
form of  •';".  e  csr  is  also  inclined  and  when  "ci-e  car  has  reached-  the  yard,  the  pile 
is  rolled  to  its  place  on  skies,.  B}7  this  method  no  large  plant s  except  the  rolling 


G    .?.?  i:'f   r-i3^<;' 


..in--: 


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.  . 

'v.'WC    irfj    :vi    Oi'il' 

''•?  i-fv'.'  T.   icnoiJj 


173 
device  is  regi  ired  to  handle  the  pile  during  its  foirativa  stage.  V/ben  thess 

piles  are  to  be  driven  into  place,  a  driving  head  is  used  and  when  jetted,  a 
wrought  iron  jetting  pips  forns  the  winding  core.  Pilesof  this  kind,  61  ft.  long, 
have  been  dciven  and  pulled  out  for  eEaminatioa ,  found  to  be  intact  and  redriven. 
Like  other  piles  of  this  class,  the;?  have  stood  very  severe  treatment.  In  one 
instance  an  attempt  was  made  to  destroy  a  pile  by  over  -driving;  later  the  pile 
was  pulled  up  and  the  only  £,pp5-,rent  injur}-  v.'as  the  rushing  ox  brooming  of  the 
upper  2  ft.  This  type  has  been  used  in  the  foundations  of  soae  of  the '.stations 
of  the  Brighton  Beach  Eailroad,  in  Brooklyn,  K,Y, ,  in  filled  ground.  It  has  also 
been  used  in  other  places  throughout  the  United  States. 

SPECIFICATIONS  -  R5IMFQBCED  COHCBETE  PILES. 
Specifications,  Reinforced  Concrete  Piles,  San  Francisco  Building  Law, 

1910,  sec. 43:-  "Reinforced  Concrete  piles  may  be  built  in  place  or  driven  after 
building  b3^  water  jet  or  by  hammer  if  the  head  is  protected  from  injuries.  The 
ratio  of  length  to  least  cross  sectional  dimensions  at  the  center  shall  not 
exceed  25.  Reinforced  concrete  piles  shall  not  be  loaded  to  exceed  350  Ib.  per 
sq.in.  of  concrete  at  middle  section..  There  shall  be  a  clear  space  of  at  leest 
one  foot  between  any  parts  of  adjacent  piles". 

The  San  Francisco  Ordinance  further  stetes:-  "Reinforced  concrete  piles 
shall  b  e  buil'c  in  accordance  with  the  provisions  for  the  construction  of  rein- 
forced concrete  in  Class  3  buildings,  as  far  as  such  provisions  apply".   Clearly 

direct  conpressive  or  column  bending  stresses  should  not  exceed  safe  values.  Bond 
between  concrete  and  stesl  should  not  be  severed  by  driving.  A  rich  mixture  of 
concrete  should  be  specified  of  proportions  at  lor.st  1  cement,  2  sand,  4  broken 
stone,  the  stone  to  pcss  a  3/4  in.  ring.  The  concrete  as  used  should  be  wet,  par- 
ticularly for  piles  molded  in  place,  It  should  be  well  rammed.  In  Hew  York  City 
where  J>iles  with  large  steel  areas  in  their  cross  sections  have  been  used,  the 
building  department  has  allowed  a  higher  bearing  •feclue  than  for  plain  concrete 
piles,  viz=,  350  Ib.  ~oer  sq.  in.  on  the  concrete  in  compression  and  4200  Ib.  per 
sc ,  in.  on  the  steel.  To  prohibit  corrosion  the  reinforcement  should  be  well 
covered  with  concrete  at  lerst  3  to  4  ins.  i*o  allowance  in  bearing  capacity  should 
be  .nai'e  for  exterior  steal  shells  since  their  life  is  doubtful. 

The  usual  -Dile  formulas  for  o  ear  ins  capacity  as  developed  for  timber 


., 
:    •:..    ...•-.•;.  .a:    '.£• 


*    -.  . 


174 
piles  do  not  give  satisfactory  results  for  concrete  types  For  concrete  piles 

jetted  to  place  the  hammer  formulas  do  not  apply  at  all.  In  such  cases  equation 
1,  Chapter  6,  may  apply.  To  demonstrate  carding  capacity  the  method  at  present 
adopted  in  the  United  States  is  to  actually  losd  the  concrete  pile  v4  th  a  test 
load  applied  upon  a  platform.  Pig  iron  commonly  produces  the  load.  Double  the 
guaranteed  load  must  not  produce  settlement. 

For  concrete  piles  sunk  by  hammer  driving  alone,  a  formula  talcing  into 
account  the  weight  of  the  piles  givts  reasonable  results.  Equation  1  represents 

Hitter's  formula: 

R  =  hj  W2. )  +  w  +  Q (1) 

s   W+Q 

in  which  R  *  the   resistance,  in  Ibs.    to  further  penetration,   W  =  the  weight  of  the 
hamner  in  Ibs.;  Q  =  the  weight  of  the  pile  in  Ibs-,   h  =  freight   of  hammer  fall-:    •• 
in  ins.,    s  =  the  penetration  of  the  pile   in  ins-by  the   last  blow. 

Consult  the  Shird  Annual  -Progress  Report  of  the   Sail  Francis  CO  Bay 
Marine  Piling  Survey;   Feb.    1923;  J>p  16-32,    for  a  discussion  of  Concrete   in  Marine 
Structures.   This  article  gives  specifications   for  manufacturing  and  driving  r : 
concrete  piles  with  timel^r  re^nerlrs  upon  the  necessary  protection  t»  imbedded  steel 
particularly  in  "ocean"  exposmre ,    for  'example,  piles  under  ocean  piers.   The  fol- 
lowing paragraphs  give  a  few  excerpts :- 

"Reinforced  concrete  .piles  ahi-11  b  e  composed  of  one-to-five  concrete* 
Each  pile  as  it  is  cast  shell  be  dated  and  no  piles  shall  be  handled  until  at 
least  40  days  after,  being  cast.   The  driving  shall  be  done  with  a  steam  hammer 
having  a  striking  part  weighing  5000  Ib.   and  a  normal  stroke  of  36  ins.  Rein- 
forcement bars  shall  be  placad  at  least,  three  times  the  bar  dimension  from  any 
exposed  surface  and  at  least  five  times  the  bar  dimension  from  adjacent  parallel 
bars.    If  specified  to  be  picked  at  less  than  the  above  minimum  depth  and  spacing, 
letal  reinforcement   in  that  pa  tion  of  the  structure  above  high  tide  and  directly 
ex  rosed  to   seawater  spray  and  air  shall  be  galvanized.   Spacing  from  exterior 
surfaces  shall b e  maintained  by  wiring  to  preccst  mortar  blocks;    interior   spacing 
by  wires  or  steel  chains  approved  by  the  Engineer". 

The  materials,   theijr  proportions  and  manipulation  are  fully  described 
and   specified.   Ths   student  will  profit  by  a  full  reading  of  the  reference.    The 
problem  of  durability  in  marine  concrete  construction  is  anclyzed.    Structures  are 
broadly  classified  as  "simple"   or  "composite"   in  regard  to  type;    and  exposure  is 
roughly  judged  as  "harbor'1   ov   :Iocean"  exposure   in  regerc1.  to  the  intensity  of 


•-.-,(' 


175 

disintegrating  conditions. 

t 

"Simple"  structures  are  understood  as  including  homogeneous  concrete 
structures  greater  than  12  ins.  in  minimum  section  and  having  no  steel,  wood  or 
other  structural  material  imbadded  at  less  than  6  ins.  from  the  surface." 

"Composite  concrete  structures  are  understood  as  including  structures 
having  ;-ie:cbers 'of  reinforcing  steel,  structural  steel  or  wood,  embedded  at  less 
than  6  ins.  from  the  exposed  sur faces" , 

"Harbor  c-xposnrc  is  understood  to  refer  to  structures  located  in  pro 
tooted  harbors  where  the  members  are  only  occasionally  exposed  to  seawater  spray 
and  arc-  well  brrcc-d  and"  anchored  against  impects.  Ocean  exposure  refers  to 
structures  located  in  the  ocean  and  opposed  to  continual  spray  from  surfaand  hecvy 
inspect  of  waves." 

Thus  for  some  cases  galvanized  reir.forcing  steel  is  reconmendod,  the 
steel  to  be  uniformly  covered  with  a  spelter  coating  of  2  1/2  oz,  of  spelter  per 
sq<  ft,  of  surface  area.  Painting  with  asphalt  of  exposed  surfaces  of  concrete 
also  is  prescribed;  part icularlyly for  "harbor"  exposure. 

PROJECTION  OF  EMBEDDED  STEEL  AND  WOOD. 

"The  principal  cause  for  the  disintegration  ofcomposite  structures 
composed. of  concrete  and  reinforcing  or  structural  steel  is  the  rusting  of  the 
embedded  steel  under  the  accelerated  corrosive  action  of  t:e  sea  water.  This 
rustjSng  takes  piece  above  mean  tide  elevation,  in  that  portion  of  the  structure 
exposed  to  both  sea  water  moisture  and  air.  The  e.ction  is  increased  by  the  use 
of  porous  concrete  and  by  the  formation  of  fine  cracks  under  impact  end  t  ension 
^iclr  assist  the  penetration  of  moisture  and  air.  It  is  retarded  and  prevented  by 
t/..e  use  of  dense,  impervious  concrete  and  by  the  sealing  of  c  racks  to  prevent  or 
retcrd  penetration.  The  action  varies  widel3'  with  the  nature  of  exposure,  'i>oing 
v?ry  rapid  in  "ocean"  structures  which  are  repeatedly  bathed  with  spray,  and 
comparatively  slow  in  "harbor"  structures  which  are  infrequently  wet  directly  by 
spray.  The  damage  consists  in  splitting  and  cracking  of  the  protective  coating 
as  the  embedded  steel  expands  on  rusting.  The  forde  of  expansion  increases  with 
the  size  of  bars  end  their  concentration,  and  for  this  reason  the  spacing  and 
depth  of  protective  coating  is  made  dependent  on  the  size  of  bar.  Because  the 
cracking  destroys  adhosion  between  the  steel  and  concrete,  mcchanicrl  bond  bars 
are  preferable  to  plain  bars.  Embedded  structure!  steelmay  be  protected  by  giving 
a  heavy  coat  of  paint,  so  that  the  salt  moisture  cannot  come  in  contact  with  the 
Steel,  but  this  decreases  the  bond.  It  is  possible  that  a  system  of  painting 
reinforcing  steel  which  will  not  seriously  reduce  the  bond  may  be  developed ,  but 
v/ith  present  experience  galvanizing  is  recommended.  The  protective  costing  for 
painted  structural  steel  and  timber  should  be  reinforced  against  impacts  with  a 
g?lvanized  wire  mesh, 

Reir.forcod  structures  having  a  "harbor"  exposure  begin  to  show  cracks 


.    ''-       "" 


•••?         •     ir    . 

••••".      -  ^v 

"£' 

-      -''  '        .'JL'~    ' 

'-•ocii.',  ;?vi- 


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176 

in  the  moi  e   vulnerable   locations  in   from  five  to   ten  years.  Many  have  been  in 
service   for    from  10  to   15  years  without  serious   frilure  resulting   from  the 
cracking,      Painting  the  exposed  surfaces  with. asphalt,   as    specified,   and  main- 
taining the  .costing  when   it  deterio^tes  will  prolong  the  life  of  these   structures 
indefinitely  and  make   them  comparable  .to  high  class  structure  1   steel  construction 
.which  is  raaintcinec"    in  a  similar  way  by  inspection  and  painting," 

The   student   is  referred  to  the   following  articles  dealing  with  concrete 
structures  exposed  to  sea  water. - 


Reinforced  Concrete  Huniciprl  Pier   at  Santa  Conies-,   California.;   by  *,  K, 


r/"arner;  Eng.  Hero..  Vol.62,   Dec.   9,1909,  p. 633. 

2.  Ocean  Pier  to  be  Scrapped  because  of  Concrete  Disintegration;  Err:,  iiews, 
Vol. 84, March  25,1920,  p. 621, 

3.  Deterioration  of  Structures  of  Timber,  Metcl  end  Concrete  Exposed  to 
Action  of  Sea  "water;  Committee  Report,  Institution  of  Civil  Engineers  of  St. 
Britain,  1920. 

4.  Effect  of  Sea  Y/ater  on  Concrete  Structures;  by  C.E.Y/.Dodwell;  Canadian 
Engineer,  Vol.39;  Aug. 26, 1920,  p.279;  comment  by  T , K, Thomps on ,  p. 359. 

5.  Articles  on  the  Effect  of  Sea  Water  on  Concrete,  by  P,,J.?/igg  and  L.R. 
Ferguson.;  Engineering  News-Record,  Vol.79,  pp.  531,  532,  641,  674,  689,  837, 
794,  1212, 

6.  Action  of  the  Salts  in  Alkali  and  Sea  Water  on  Cements;  Technologic  ?&p. 
Bureau  of  Standards,  No.  12,  by  Bates,  Phillips  and  Wigg;  1912. 

7.  Tests  on  the  Absorptive  and  Permeable  Properties  of  Portland  Cement 
Mortars  and'  Concretes  Together  with  Tests  of  Dempproofing  and  Waterproofing 
.Compounds  and  Materials,  U.S.  Bureau  of  Standards,  Tech.  Paper  No.  3,  by  Wigg  and 
Bates,  1911. 

8.  The  Use  of  Wood  and  Concrete  in  Structures  Standing  in  &9a  Water,  by 
E,  S. Taft,  Trans.  Internat.  Eng,  Congress,  Sen  Francisco,  1915,  Vol.X,  p. 321. 

9.  Concrete  Test  Specimens  in  Seawatar  at  Charleston  i.avy  Yard.;  Errv.  Record, 
Vol.64,  Aug. 19 ,1911,  p. 229, 

10.  A  Four-Year  Test  of  t£s  Effect  of  Seswater  on  Concrete;  Ens.  News, Vol. 70, 
Nov. 20, 19 13,  p. 1093. 

11.  Action  of  Seawater  or.  Concrete;  Results  of  Six-Year  Pesos  of  23  Molded 
Piles  of  Various  Mictures  Sub  erged '.in  Boston  Harbor  anc?  Withdrawn  Periodically 
for  Examination;  Eng.  Rec.  Vol.69,  March  21,1914,  p. 344, 

12.  How  to  i'lake  Concrete  Resist  Action  of  Seawater;  Eng.  Record,  Vol.73, 
May  27,1916,  p. 702. 

13.  The  Application  of  the  Perforating  Process  in  the  Preservative  Treatment 
of  Wood  with  a  Special  Reference  to  Douglas  Fir,  by  ;:,,M,  Blfke,  Journal  of  the 
Boston  Society  of  Civil  Engineers,  Vol.7,  No.  4,  April  1920  p. 99. 

14.  Preservation  of  Piling  Against  Iferine  \7ood  Borers;  S-C, Smith;  U, S.Dept, 
Agr  ,  Fforest  Service  Circular  123,  Jan. 23. 1908. 

15.  Recommend  Concrete  for  Oces.n  Structures  at  New  York;  Err,-.  News- Record, 
Vol.86,  June  15,1321,  p.. ±052. 

IB.  More  Observations  of  Effect  of  Sea  Water  on  Concrete;  Eng.  iiews -Record, 
Vol.86,  Jan. 20, 1921,  p.  121. 

17.  Deterioration  of  Structures  in  Sea  Water-,  Second  Interim  Report-,  Com.  of 
Inst.  of  C,  E.  of  Gt.  Britain ,1922. 

18.  Concrete  Piles;  E, J.Cole,  Trsns.  Am.  boc.  C.E. ,  Vol.65,p.4&7,  1903. 

19.  Concrete  and  Reinforced  Concrete  Construction,  R,^.Reid,  Ed..  1907 ,•  p. 428-464. 

20.  Concrete,  Plain  and  Reinforced,  Tailor  &  Thompson,  ed.  1909 ,p, 650-656, 

21.  Reinforced  Concrete,  Buel  &  Hill,  ed.  1906,  p. 162-174. 

22.  Construction  and  Use  of  Concrete-Steel  Piles  in  Foundation  Work..  Sng, 
Fev/s,Vol.51,p.233,  Ivlarch  10,1904, 


•?•:*&.  ".."•",  — 

«•••  ••    C  .'  ""••• 


177 

23.  References  to  articles  on  concrete  piles,  Eng.li'ev/s,  Vol.54,   p. 594, 
Vol. 62, p. 684-5,   Vol.63,   p. 30, 411;  Ens-  Record,  Vol. 60 ,p, 656,  Vol.61, y. 218, 

24.  Soine  Experiences  v/ith  Concrete  Piles   in  Chicago;   J, K.Jensen;  En~.uews, 
Vol.69  ,p.4$6. 

25.  Hair  forced  Concrete  Piles  on  t::e  Chicago,  Hock  Island  and  Pacific  F.,R. , 
Eng.  Record,  Vol.67,  p. 606. 

PROBLBLiS 

1.  Describe  concisely  the  essential  features  of  the  following  types 
of  concrete  piles:-  (a)  corrugated,  (b)  Simplex,  (c)  Raymond,  (d)  Kennebicue, 
(e)  Cole,  (f)  Pedestclo  Give  c.s  far  cs  possible  your  idea  of  their  relative 
advantages  and  disadvantcnjes, 

2o  A  concre'ce  pile  48  ft.  lon^,  square  section.,  20  ins.  side  or  butt 
tapering  to  10  ins.  r.t  point,  is  driven  by  a  5000  Ib.  ha/.ner  felling  15  ft. 
per  blow,  Un'"sr  the  last  five  blov;s  the  pile  penetrates  a  total  of  2  3/4  ins, 
Fird  the  prob£.ble  resistance  to  further  driving  by  Hitter's  fornula.  Cf.  Trans. 
A:-i.  Soc.  C.Eo,  Vol.65,  p. 470. 


178 

PART  II 

FOUMDATIOKS  UICDER  HATER 
See  Also  Chapter  3, 

The  subjects  discussed  are: 

Chapter  8       Concrete  Deposited  Under  T/ater 
Chapter  9       The  Coffer  Dam 
Chapter  10     Open  Caisson;- 
Chapter  11     Pneunr.tic  Caisson 
Chapter  12     Deep  V/ell  Dredging 

CHAPTER  8 
CONCRETE  DEPOSITED  UNDER  V.'ATSR 

The  construction  of  foundations  by  any  of  these  methods  frequently  is 
facilitated  if  not  made  possible  by  the   deposition  of  concrete   in  mass  under 
water.    It  has   often  been  contended1,  by  engineers  that  such  deposition  v;ill  not 
yield  reliable  results,   particularly  in  sea  water.   The  objections  are  mainly 
based  upon  the  difficulty  experienced  in  depositing  concrete  under  v/ater  without 
w.ashin~  the   cement  out  of  the  mass,   thus  leavin  :  an  inert  residue   of  sand  or 
;;ravel  and  broken   stone   in  place   of  a  continuous  volume   of  sound  masonry. 
Ample  experience  however  in  connection  with  successful s tructures  has  demon- 
strated the  feet  that  concrete  ;.i£.y  be  deposited  under  v/ater  so  as  to   set  in  a 
hard  and  ei'durin^  mass  with  satisfactory  resisting  capacity, 

Tliere  are  a  number   of  conditions  requisite   for  such  results  end   they 
ere  v/ith  care  practicable  of  attainment.   They  are   as    follov/s:- 

1.  The  space  within  which  the  concrete   is    to  be  deposited  must  be  so 
completely  enclosed  that  the  water  shall  be  entirely  without  current, 

2.  A  rich  Portland  cement  concrete,   not   leaner  than  one  cement,   two 
sand  and   four  b  roken  s  tone  . 

3.  A  properly  designed  bucket,   preferably  cubicrl  in  shape,  v/ith  a 
tripping  bottom  so  arranged  to  b  e  alv/eys  under  control  and  permit  the  concrete 

to  escne   in  one  .nass  v/ith  the   least  possible   disturbance.   The  bucket  used  shoulc', 
be  the   largest  which  the  dimensions   of  the  work  will  peroit,  preferably  in  no 
case    to  hole    less  than  one  cubic   yard  and  as  much  more  as  practicable.    The   ton 


II  i'-i.-l'j 


<.r.C.    so'i 


ri.'i.,,,'    ."io-'-^a 


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;'¥-     ->.'•,:        «'.-}-, 


179 

of  the  bucket  may  well  be  protected  by  a  perforated  <?over  which  should  be 
raised  before  the  bottom  is  tripped.    Fig.   57. 

4.  The  bucket  must  be  lowered  uniformly  and  not  too  rapidly  in  a  ver- 
tical direction  only  and  be  held  for  a  moment  just  at  the  surface   of  the  water 
to  enable  any  air  held  in  the  voids  of  the  concrete  to  escapfc. 

5.  The  concrete  must  be  thoroughly  mixad  v;et  so  t  s  to  reduce  the  voids 
with  their  enclosed  air  to  a  minimum. 

6.  When  the  volume  of  the  work  is   considerable,  the  concrete  must  be 
deposited  in  uniform  layers  with  their  surfaces  inclined  downv/ard  to  a  central 
point,   from  which  the  laite.nce  is  to  be  removed  carefully  by  a  hand  pump  if 
necessary. 

7.  The  process   of  deposition  must  be  carried  on  continuously  from  the 
beginning  to  its  completion. 

8.  The  bucket  must   be  tripped  only  when  it  rests  solidly  on  the  concrete 
already  in  place,   so   that  the  concrete  being  deposited  shall  have  absolutely 

no  free   fall ,  whatever  through  the  water. 

Large  masses  of  concrete  have  been  deposited  where  these   conditions 
have  been  scrupulously  maintained  with  most  excellent  results,  \7hen  the  water 
lias  been  pumped  out  of  the  cofferdam  enclosure  the   general  naass  has  been   found 
to  be  practically  all  that  could   be  desired.   There  will  usually  be  a  few  s oft 
pockets  of   laitance  b$rt  too    few  and  small   in  size  to  exercise  any  influence 
upon  the   carrying  capacity  of  the  whole  ;nass. 

Under  circumstances   in  which  it   is  necessary  to  deposit  concrete  by 
allowing  it  to   fall  through  the  water  or  in  a  current,    it   is  necessary  to  use 
bags  of  canvas,   cheesecloth  or  other  similar  loose  fabrics,   so    that  washing  of 
the  concrete  will   be  prevented  to  any  material  extent,   at  the  same   time  giving 
the  cement  opportunity  to   find  its  way  through  the  fabric  of  the  bags..  The 
latter  will  then  be  well c  emented  together  where  they  lie   one  on  anothei  .   Paper 
bags  are  also  sometimes  successfully  used.  After  the  bags  are  in  place  the  water 


•    •••:',    ..-.  ."v:-  .  ::•..    :-        '.   <      •  • 
.   y-l      &'•'.  '  ,    "i    .', ..    '.-.:    :.<-.:.    : 


r1    >;  .  -f  (•.--! 


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180 

*• 

scales  away  enough  of  the  paper  to  enable  the  contents  of  the  bags  to  unite  into 
a  coherent  mass;  that  is,  such  a  result  will  follow  if  the  ba-s  are  properly 
handled,  and  if  the  paper  is  of  the  proper  texture.  When  ba^s  are  used  they  may 
hold  1/4  to  1/2  a  cubic  foot  er.ch,  and  they  should  not  be  more  than  2/3  filled 
in  order  that  they  may  to  some  aster. t  mould  themselves  into  each  other  and  form 
as  nearly  as  possible  a  solid  mass. 

Concrete  has  been  deposited  under  water  in  different  ways: 

1.  3y  usin~  ba^s  of  paper  or  canvas;  En;:.  Hews,  Vol. 28, p. 379. 

2.  Through  adjustable  chutes,   (tremie  concrete) 

3.  V/ith  tripping  buckets 

4.  Depositing  i ->  molds  under  water;  Ln{j.  Nev/s,Vol.53,p.232. 

Examples  of  (Joftcrete  Deposited  Under  Y/ater 

1.  Concrete  Deposited  by  Chute*   In  En;;..  Eews,  Vol.39,  p.  181,  there  is 
a  description  of  concrete  deposited  under  seawater  for  the  Charlestown  bridge 
piers,  Boston,  I.Iass.  Consult  also  the  third  annual  report  of  the  Boston  Transit 
Commission.  The  concrete  piers  rest  on  pile  clusters.  The  contract  required  al- 
ternate ranges  of  bearing  piles  to  be  cut  off  at  different  ^rcdes.  The  first, 
third  and  fifth  rows  were  cut  off  18  inches  above  the  bottom  of  the  excavation; 
tl:s  second-,  fourt?-.,  sixth,  etc.  were  cut  off  10  ft.  below  low  v;ater;  these  latter 
rowsnot  being  cut  until  s  6  ft.  layer  of  concrete  had  been  deposited  over  the 
bottom  of  the  excavation.  The  lowr-level  piles  were  driven,  then  cut  off  by  a 
circular  saw,  before  the  hi-vh  level  piles  were  plr.ced.  Before  the  hi'jh  level 
piles  were  cut  a  cofferdam  of  Wake field  triple  lap  sheet  piling  was  constructed 
around  the  proposed  pier;  this  cofferdam  consisting  of  2  in.  spruce  planks  bolted 
or  nailed  together.  Perusal  of  the  r eferences  will  explain  variations  in  the 
design  of  cofferdams  for  different  piers.  Clay  and  stone,  were  dumped  outside 
the  dams  to  fill  that  part  of  the  excavation. 

These  cofferdams  formed  a  mole1,  or  box  for  tl-e  deposit  of  concrete  upon 
and  about  the  piles.  The  concrete  -.lasses  extended  5=39  ft.  below  mean  low  water 
the  top  foot  in  depth  of  the  concrete  laid  after  the  coffer  dam  hc.d  been 
d  out.  The  concrete  was  made  of  1  -part  English  Portland  cement,  2  parts 


*>r=,  c.  J.  '     •  .:*;.'    .;  '    •'--=•  uO»    L.  r '.''  ?it 


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C-".'i::v;.^    ,'iiTT.. 


191 

clean  sharp  said,   and  5  parts  gravel  dredged   from  the  harbor.   The  concrete  was 
mixed  in  a  continuous  mixing  .nachine  with  inclined  su:is. 

The  concrete  was  deposited  under  water  through  a  cliute  or  tube   14  ins. 
In  diameter  at   the  bottom,    11  ins.    at  the  neck,  v/ith  a  hppper  r.t  the   top  to 
receive  the  concrete.   The  tube  was  mr.de  in  removable  sections  with  outside 
flrnges  to  adapt   it  to  different  depths.    It  vr.s   suspended  by  a  differentir.l 
hoist   from  r.  true!:  moving   laterally  mounted  on  p.  frame  which  could   travel  the 
length  of   the  pier, 

In  operation  the   foot  of  the  chute   rested  on  the  bottom.    The  concrete 
was  dumped  into   the  hopper.   The  chute  was   then  slov/ly  raised  ~nd   the  concrete 
allowed   to  run  out   in  a  conical  heap  vhils   the   loss   of  concrete   in  the  tube  wr.s 
mrde    good  by  dumping  in  more  concrete  r.t  the   top.   Thus.,   as   the  t  ruck  moved  on 
the  traveler  a  ridge   of  concrete  wr,s.  deposited  across  the  pier,   the  chute  being 
r.lwr.ys  kept   full,   or  nc-rrly  so,   by  dumping  in  .nore  concrete  at   the  top. 

Uhen  a  ridge  was   finished  the  traveler  wr.s  moved  and  another  ridge 
built.-   '""'en  the  v/hole  ,-rer.  of  the  foundrtion  hr.d  been  covered  c.  nev;  Dr. yer  \vr.s 
deposited  on  it  r.s   soon  r.s   the  first  .hr.d  sufficiently  hardened.    It  was  thought 
thr.t  the  best  r  suits  v/ere  secured  v/ith  Ir.yers  2  1/2  ft.   thick,   though  some 
courses  v/ere   Ir  id   6  ft.    in  thickness,   if  the   br.nlc  v;r.s   too  hie"."-  or  uneven,    or  the 
chute  moved  or  rr.ised  too  Quickly,  the  clT.rge  of  concrete  wr.slost  and  the  water 
rose   inside    the  chute  to  the   level  of  thr.t  outside.    In  these  cr.ses  the  concrete 
first  dropped  in  wr.s   liable  to  v/r.sl".    so   that  separation  of  the  s  and.   from  the 
cement  followed,   The  s'.me  condition  resulted  when  the  work  was  stopped,    since 
•the  concrete  v/ould  otherwise   set   in  the  chute.    It  usually  took  about  one  cubic 
yard  of  concrete  to  replace  the  water  in  the  chute,  which  amount  wr.s   in  danger 
of  giving  badly  washed  concrete =   AS  the  inspector  grined  experience,   accidentrl 
losses   of  the  charge  became   infrequent.  After  an  intermission  work  was  commenced 
near   the   center   line   of  the  pier  so   that  any  bad  concrete  would  be  surrounded  by 
good.  A  canvas  piston  was  devided  to  keep  a  first  charge   from  dropping  too 
rapidly  tLroujh  the  water.    Its  cost  was  considerable  anc"   its  use   abandoned. 


ff   ; 


J'.\f  .• 


;    .     .    . 


182 

The  chute  seemed  to  work  best  when  the  concrete  was  mixed  not  quite  moist 
enough  to  be  -plastic.  If  mixed  too  wet  the  charge  was  liable  to  be  lost  and  if 
very  dry,  there  was  a  tendency  to  choke  the  chute.  An  excess  of  grrvel  permitted 
the  outside  water  to  tforce  its  way  in  at  the  bottom  and  an  excess  of  sand  tended 
to  check  the  flow  of  concrete. 

TRH.IIE  CONCRETE 

In  tae  past  decade  tremie  concrete  has  been  more  and  more  frequently  used 
as  distinguished  from  concrete  deposited  in  mass  by  bucket.;  for  example,  in  tunnel 
vork.  The  Detroit  tunnels,  consisting  of  units  of  structural  steel  shells  sunk  in 
o-^en  excavation  were  covered  on  bottom,  sides  and.  top  with  a  concrete  mass.  See- 
Trans.  AIVI.  Soc.  C.E. ,  Vol.74,  p.  288,  Plate  43  and  Fig.7.  The  proposed  tunnels 
under  the  Estuary  at  Y/ebster  St.,  Oakland,  California,  are  tentatively  designed  to 
consist  of  units  of  reinforced  concrete  shells  about  200  ft.  Ion;;  each,  to  be 
'oulkheaded,  floated  to  place  and  sunk  in  open  excavation.  After  joints  between  the 
sections  have  been  sealed  inside  and  out,  the  tube  is  to  be  covered  where  necessary 
with  masses  of  concrete  probably  to  be  deposited  by  trsTue. 

The  processes  of  deposi  tin^  concrete  by  tremie  have  been  gradually  improved 
so  that  now  the  objections  to  this  method  are  not  so  serious  as  heretofore,  when 
cornpE. red  with  the  deposition  of  concrete  by  bucket. 

Reference  has  alrerdy  been  :.iade  to  the  Third  Annual  Progress  Report,  San 
Francisco  Bay  Marine  Piling  Survey;  the  articles  on  "Concrete  in  I/Ir.rine  Structures"  * 
p,  16-32.  Article  8  from  Section  C,  ;1The  Manipulation  of  Concrete"  reads  as 
follows:- 

"Concreting  Under  Y.ater.  Concrete  shall  not  be  deposited  in  sea  water  or  under 
the  sea  water  unless  authorized  by  the  Engineer.  Y.Tien  placed  in  sea  water,  concrete 
shall  be  discharged  through  a  water  ti^ht  tremie  into  prepared  pockets  of  such 
capacity  that  each  can  be  completed  without  interruption  of  the  flow  of  concrete, 
The  treraie  pipe  shall  be.  of  sufficient  size  to  permit  the  free  flow  of  the  plastic 
concrete,  and  the  arrangement  shall  be  such  that  the  t.emis  can  be  readily  raised 
or  lowered  without  interruption  of  the  flow  from  r  hopper  or  .-ixer  until  the  pocket 
is  completed.  The  size  of  pipe,  dimensions  of  pockets  and  capacity  of  hopper  and 
mixer  shall  be  determined  by  the  Zirjinesr  and  will  d epend  upon  the  depth  of  water 
and-  the  size  of  dimensions  of  the  pockets  to  be  filled.  In  operating,  the  top  of  the 
tremie  pipe  shall  be  plugged  with  hay  or  straw  to  be  forced  ahead  of  the  charge  of 
concrete. \\fter  the  charge  is  strrted,  the  flow  of  concrete  into  the  t remie  shall 
be  carried  on  continuously  v.lthout  interruption  until  the  pocket  is  completed. 


..,;  v.'i-y.. 


:^'"  '-   •' 


^'"   •  ^ 


btr 

;  •    .•'.       •; 


•*"'    >.o    /•".    :~' 


183 

lower  end  of  the  treraie  pipe  shall  be  kept  embedded  in  the  concrete  to 
such  a  depth  that  -water  c  annot  be  forced  back  into  the  pipe  through  the  plastic 
concrete . 

Tremie  concrete  shall  be  proportioned  at  least  one  part  cement  to  four  parts 
aggregate.  The  consistency  of  the  concrete  shall  be  mushy  so  that  it  will  flow 
readily  without  s  eparation". 

2.  Concrete  Deposited  by  Bucket.  A  description  of  methods  used  for  de- 
positing concrete  in  seowater  for  the  pivot  pier  of  the  Karlem  Ship  Canal 
Drawbridge,  New  York  City, /jiven  in  the  next  chapter  on  coffer  dam  construction. 
See  figures  57,  58,  59.  In  this  method  a  bucket  with  tripping  bottom  was  employed; 
sea  also  Engineering  News,  Vol.31,  p. 349. 

In  Engineering  News,  Vol.42,  p.  405,  Mr.  J.  F.  O'Rourke  describes  a 
bucket  which  was  used  for  placing  concrete  underwater,  constructing  foundations, 
City  Island  Bridge,  New  York  City.  These  piers  are  of  concrete  faced  with  li  ie- 
stone  ashlar  and  granite  copings  in  their  visible  portions.  They  rest  upon  rock 
bottom  in  depths  of  s  eawater  averaging  20  to  30  ft.  below  mean  high  water.  The 
nonmal  tide  range  rs  8  ft.  Between  City  Island  and  the  mainland  is  a  tidrl  strait 
of  considerable  current  velocity.  There  was  little  surface  material  over  the 
rock  bottom  except  bouldors.  Tho  pier  concrete  was  deposited  in  wocden  coffer 
dans  similar  in  construction  to  fig.  38.  The  O'Rourke  bucket  is  an  improvement 
on  fig.  57;  for  an  illustration  see  Taylor  &  Thompson,  Concrete:  Plain  and 
Reinforced,  p.  306.  The  bucket  is  rectangular  with  a  V-shrped  bottom  consisting 
of  two  flap  doors  similar  to  those  in  fig.  57;  but  there  r.ro  two  other  desirable 
features:-  1.  the  lower  edge  has  a  timber  frame  which  Gives  r.  vide  bcr.rinc;  when 
the  bucket  rests  on  the  soft  deposited  concrete,  which  prevents  its  sinking  into 
and  cutting  the  concrete.  Between  the  cutting  edge  end  the  hinges  of  the-  flap 
doors  two  sides  of  the  bucket  box  cue  open,  allowing  er.sy  flow  of  wr.ter  in  r.ncl 
out  of  the  bucket  bottom  as  the  flap  doors  open  or  close,  thus  giving  the  least 
eddy  disturbance  as  concrete  is  dropped;  2.  at  the  to~o  the  bucket  has  flap  doors 
which  are  closed  when  the  concrete  is  b eing  deposited;  they  also  reduce  the 
action  of  currents  or  eddies,  The  top  and  bottom  flap  doors  rre  operated  auto- 
matically. The  obvious  advantage  of  this  bucket  for  depositing  concrete  under 
water  is  that  it  does  not  let  the  material  fall  through  the  water  and  that  it 


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184 
operates  to  shut  out  water  from  the  concrete  charge  until  the  concrete  is  finally 

in  position. 


MiSSES®,'   Bhere  concrete  is  deposited  in  water  there  should  be  no  stream 
or  tidal  current  and  no   local  churning  or  eddying  of  thev.-ater  through  careless 
depositing  of  concrete.   Still  v/cter  is  produced  by  proper  designs  of  coffer  dams 
or   sheet  piling  enclosures.   Local  churning  or   eddying  is  reduced  to  a  minimum 
through  the  use   of  bags,   chutes  or  buckets   for  depositing  concrete.   Even  with  the 
greatest  precaution  the  concrete  will  be  somowhr.t  disturbed,    forming  laitance. 
When  concrete   is  deposited  under  water  carelessly  much  laitance   is   formed. 

A  number  of  piers  built   in  San  Francisco  Harbor  about   1904   or   earlier 
rest  upon  cluster  piles  whose  heads  are  protected  by  reinforced  concrete  deposited 
in  cylinlric  v;ood  stave  coffer  dams,    see    fig.  49.    In  later  years  many  of  these 
piers  have  been  inspected  and  in  some  cases  the  cluster  piles  were  found   to  have 
highly  defective  concrete   tops.   Uherever  the  stave  coffer  dams  were  driven, 
sealed  at  the  bottom,  pumped  free   of  water  and  dredged  of  soft  material,   so  that 
the  concrete  could  be  deposited  around    the  pile  heads    in  the  dry,   the   work  is 
found  upon   inspection  to  b  e  scvrird'and  first  class.   Bat  where  the   core  ret  e  was 

•iff* 

deposited  into  such  cylinders  without  first  pumping  out  the  water  .,  it  apper.rs 
thr.t  it  was  practically  impossible  to  produce  first  class  concrete  work.  The 
presence  of  expanded  metal  or  other  reinforcing  material  within  the  cylinders 
together  with  the  presence  of  the  pile  heeds  crusel  too  much  disturbance  of  the 
concrete  as  it  was  dropped  through  the  water,  separating  the  cement  fnari  the  sand 
and  aggregate,  producing  grert  mrsses  of  inert  soapy  Rdr.terir.lsbr  Ir.itarsce.  As  the 
wood  stave  cylinders  decayed  the  concrete  was  found  di  sintegrrted  and  ciumbled 
away  lerving  the  wood  pi'..es  bare  and  the  dock  floor  un  -supported. 

YThere  concrete  is  deposited  in  still  water  rn  coffc-.r  dams  ,  like  fi'js.r 
38,  39,  59,   rind  65,  it  is  well  to  plr.ce  the  concrete  in  layers  with  tha  top 
surface  sloping  from  the  outside  tov/rrd  the  center  of  the  p-'.er  or  cofi'pr  dan 
enclosure  so  thrt  lu:.ritaacG  v;hich  forms  may  flow  or  be  swept  toward  th<?  center 
ard  be  i  amoved  rt  irrcervals. 


185 

Laitance  is  decomposed  cement  formed  in  the  presence  of  an  excess  of 
water.  The  word  is  of  French  origin  but  quite  generally  adopted  in  the  United 
States  and  England  for  the  light  colored  powdery  substance  which  is  held  in 
suspension  by  water  when  cement  or  concrete  is  deposited  below  the  surface.  ?/hen 
ever  concrete  is  Irid  under  water,  the  water  is  likely  to  b e  clouded  by  what 
appears  to  be  particles  of  c  ement  floating  up  from  the  mass  which  is  being  laid. 
A  similar  formation  tends  to  cc  cur  on  the  surface  of  concrete  laid  in  the  dry' 
with  a  large  excess  of  water.  Laitance  has  nerrly  the  same  chemical  composition 
except  for  loss  on  ignition  as  normal  Portland  cement,  but  consists  ir.  rgely  'of 
amorphous  material  of  an  isotropic  nature.  It  has  almost  no  setting  properties. 
Therefore  when  concrete  or  mortar  is  laid  under  water- or  with  a  large  excess  of 
water  a  portion  of  the  cement  is  tendered  incaprble  of  setting  and  the  strength 
of  the  concrete  mass  is  consequently  reduced  in  proportion.  Where  concrete  is 
laid  under  water  or  vith  large  excess  of  water  in  mining  there  should  be 
specified  a  higher  percentage  of  c  em'ent  tl-an  usual,  about  one-sixth  more.  A 
lean  mixture  is  more  serious^  injured  by  an  excels  of T-  r  ter  than  a  rich  one. 
For  further  study  of  Ir.itance  consult  Taylor  arid  ^'.-lo.'-.ipscr..  Concrete:  Plain  and 
Reinforced,  pp.  2c,  303,  384. 

Additional  References:  Placing  concrete  oru  er  v-.-.sr,  Engineering  Sews, 
Vol.  24,  p.  548,  p.  575;  Vol.  ol,  p.  131;  Vol..  35,  p.  127;  Vol.  43,  p.  26; 
Vol.  46,,  p.  275;  Vol.  50,  p.  25V;  Vol.  62,  p.  58'5,   T.-r;lor  £•  Chomps  on,  Concrete 
Plain  and  Reinforced,  edition  1909,  pp.  301-2 


:J. 


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- 


186 

CHAPTER   (9 

COFFER  DAMS 

Pivot  pier,  Karlem  Shi]2.  Cartal   Bridge.      The  application  of  the  coffer 
dam  process  for  constructing   foundations    on  a  hard   or  rode  bottom  is  well  illus- 
trated in  Fig. 59.   The   plan   there  shown  was  used   to  construct  the   draw-sprn  pier 
of   the  Harlem  Ship  Canal  Bridge   situatec1  at   the  north  end  of  Manhattan  Island  in 
New  York  City.    It   is  typical  of  a  successful  treatment  upon  rock  bottom  in  con- 
siderable depth  of  water  where  very  strong  tidal   currents  were  found  at  certain 
stages  of  the   tide- 

The    greater  portion   of  the    foundation   bed  lies  on   the  roughly  levelled 
rock  bottom  of  the   canrl,  but  a  portion  on  the    east   sice  reaches   over  the  natural 
slope  of  the  rock  surface.  The    canal  is  a  rectangular  prism  cut  mainly   through- 
rock  in  the   vicinity   of  the   bridge.    The  entire  foundrtion  bed  was  covered  with 
mud  and  silt  which  l:ad  flowed  over  the   rock  to  a  depth  o  f  3  to    5  ft,    The  mud  and 
silt  were  cleaned  off  by  dredging  before   the  timber  work  of  the  coffer  dam  ras 
floated   into  place, 

Two  concentric  thirteen  sided  polygonal  walls    of  timber,   strongly  braced 
(Fig. 59)  4  ft.    6  in.    apart,  were  built   in  the  water  with   the  bottoms   shaped  to 
fit   t--e  rock   foundation  bed  rs   closely  as  possible.    In  thiscr.se  the   rock  bed  had 
very  little  solid  material  or  debris  upon  it;    and.  that  little  wrs  dredged  off  as 
thoroughly  as  practicable.   Hrd  there  been  deep  mud,  srnd  or   other  material  over 
the  rock  bottom,    it  first  would  have  been  carefully  cleaned  away  by  dredging  or 
-other  means.  As    shown    in  the   plans,  the    lower  portions    of  the    timber  v.r-lls  were 
constructed  of  12  in,    by  12   in.    sticks  and  the   upper  portion  of  8  in.   by  12  in. 
and  6   in.   by  12   in.   timber.   The   1  1/2  in.    bolts  runvjin"  through  the  timber  walls 
and  the  timber  struts   between   them,  held  the   two    frc  ,ies  rigidly  at    the  proper 
distance  apart.  Almost  any  sound  timber  will  serve    for    such  temporary  construction. 

After  the  polygonal  structure  wr.s  completed   it  was  towed  to   its  proper 
position  r.nd   secured  accurately  in  place  by  suitable  timber  platforms   rnd   braces 
about   it.   Temporary  flooring  was  then  plrced  r.t  a  number  of  points  on  its  top  for 


A'  '•'-'  •-'•  ••>       J'.':;'":   ••"  r.       jiir    ;  •  ;'..•: 


.,„    J  '•:.•     -Jc.eS    r.  o3       •    .    3:.'.:     >-•/  :    ;:-,•-. 
;.    ,•       ..  •.       •  •  »r3    f".?'--"-^    ;•'•'•  ;-  -"^    '• 


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•  •.».-.(•'      ;.-     . 


187 

the  puipose    of  receiving  sufficient    loads  of  stone   to   sink  it.   3y  these   means   it 
was  accurately  and  solidly  sunk  to  the   foundation  bed. 

After   it  was   sunk  to  place  the  laver  edges  of  the   timber  walls  were 
carefully   examined  by  the   aid    of  a  diver  and   other  appropriate  means   in  order 
to  locate  any  openings   that  might    exist  under  the' bottom  of  the  dam  due   to   im- 
perfect   fitting.  The  greatest    of  these   openings  was  only  a    few  inches  in  height. 
All  the   openings  were   then  closed  by  depositing  caa^as  bags  each  containing 
about  5/4  cu.    ft.    of  concrete   in  them  under  the   inner  shell  and  similar  bags  of 
sand  under  the   outer  shell.  After  the    deposition  of  the   bags   of  concrete  under 
the  inner  shell  a  few  buckets  of  concrete  were  deposited  en  masse  over   them 
immediately  inside   of  the   enclosure.    These  operations  completely  closed  all 
openings  between  the    foundation  bed  and  the  exterior  waters  of  the  canal  and  also 
prevented   from  flowing  inwards  under  the   inner  shell  any  clayey  material  and 
gravel  which  might   otherwise  have  found   its  way   from  the  annular   space  between 
the  two  walls    of  the  dam  to  the  central  enclosure.   The   bags  of  cement  raid  s  and 
were  carefully  deposited,  a  diver  being   sent  dorm  to   arrrnge  their  positions  to 
completely  fill  the   openings  between  the   coffer  dam  shell  and  the  rock. 

The  annular  space  was  then  filled  up  to    the  ale  vet  ion  of  high  water  with 
a  mixture   of  dry  or   loam  and  gravel.  I-.'o  particular  care  was  taken  to  attain  any 
special  mixture.   The   gravel   mr.y  have  baen   from  1/3  to   1/2   of  the   vhole  mass,   This 
material  was    simply  dumped  into  the   wrter  contrir.od  ?.n  t^e  annular  volume  thus 
puddling    itself  as    it    settled  to    the   bottom.  A  gravel  mixture    such  as  that  de- 
scribed is   probably  as    good   as  anything  that   can   '.50  used   for  the  purpose.   Pure 
clay  is  not  well   adapted,  to    such  v,ork .    If  a  cuvre.-t   of  wrter  however   snail  finds 
its  way   through  a  bank  of  thrt  ;rf  terial,    it    will  grr dually   and  continuously  wash 
the  passage   larger  until  serious  damrge  and    possibly  the    failure   of  the   con- 
struction takes  place,    The   gravelly  mixture   of  dry  or  dry  rrd   lorm,   not   less 
than  1/5  being  a  gravel,      net   too  coarse,  makss  r  'very  solid  end  resistant  dam. 
If  r    small   current   finds    its   w.y   through  at  any  point,    the    gravel  vlll  quickly 
'o   into   the   passage  ard  obstruct   it  so   that   it   is  not  apt  to    grow  Irrger  c.nd 


•..-.:      •     :-i,~r,f    .s* 


fjo  -  .  •  : 


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186 
frequently  fills  itself. 

Before   the  coffer  dam  was  thus   completed,   openings  each  4  in.    in  diam. 
extending  from  the  enclosure  to  the   exterior  of  the  cr.nal  were  i7T.de  at  an  eleva- 
tion not  higher  than  mer.n  low  water  in  order  that  the  water   surface  might  rise 
ard    fall  in  the  enclosure  with   that  exterior  to  it.   If  this  were  not  done,   the 
rise  and   fall   of  the   tide  would   force  currents  undernerth  the   dam   in  and   out  of 
the  enclosure,   in  consequence  of  the   unbalanced  head  which  would  result  from 
varying  stages  of   the   tide. 

After  the   dam  VE.S  completed  the  concrete  mass  immediately  overlying  the 
foundation  bed,    as  shown  in  Fig. 59,  was  deposited  in  place.    This  deposition  vies 
Made  observing  all  the  precautions  described  in  Chapter  8.   The  concrete  mixture 
consisted  of  1  Portland  cement,  2  sand  and  4  broken^stone.   The  'bucket  used  con- 
tained 1  cu.   yd.    and   is   shown  in  Fig.  57.    It  was  tripped  in  the  manner   illustrated 
after  resting  solidly  on  the   bottom  at  any  desired  place.    Its  arrangement  was 
such  that  the  concrete   slid  out   of   it  with  the    least  possible  amount   of  wash.   The 
depth  at  mean   high  water  was  24  ft.   and  the   layer   of  concrete   about  -9  ft.   thick. 
Herce   the  weight  of  concrete  was  not  sufficient  to  completely  overcome  any  tend- 
ency to   flo\tation  produced  by  the  water  being   forced  underneath  the   concrete 
ard  along  the   foundrtion  bed  when   the   enclosure  was  pumped  out.  Enough  of  the 
blocks  of   limestone  which  were  to   be  used  in  tho  face  masonry  of  the  pier  vcrc 
then  lowered  upon  the   concrete   to  rrakc   it  certain  that   the    latter  could  not  rise 
after  the   completion  of  the   pumping.    Throughout   the    deposition  of  the   concrete 
which  was  carried  on  continuously  night  ard  day    from  beginning  to  completion-, 
the  upper  surface  was". inclined  towards  the  center   so  that  any  laitanco  which 
might  be   formed  would  flow  to   that   depressed  point. 

Before  proceeding  with  the   deposition  of  concrete  within  the  coffer  dam 
an  annular  surface   on   the    foundrtion   bed  8    ft.    wide  extending   around   its   entire 
circumference  just  inside   the   dam  was  cleaned  of  dirt  ard   loose  material  by  a 
scraper,   Fig«-58,  to    enable  a  closo   bond   to   be    formed  bctwe:n   concrete   rr_d  bedrock. 
The    screper  was  worked  by  ropes  running  over  blocks  held  at  suitable  points 


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around  the  dan  and  running  to  a  hoisting  engine,  'art   it  was  ^idec^  by  fend,   The 


or 


loose  material  was  thus    cleaned   from  the  annuls  surface  and  scrapec  in  tcwrrd 
the  pier  center  where   it   v^s  filled   into  buckets  by  divers  r.nd  removed.    The 
bond  between  the  concrete   to    be  deposited  and  the    bedroc!:  was  by  this  merns 
secured  throughout  a  surface  at  least     8  ft.   wide  around  the   circumference   of- 
the  pier  brse,    Tfee  central  portion  of  the  bed  was  clerned  but  with  less  care. 
After  the  concrete   had  been   allowed  to   set  r.early  5  weelcs  the  hole; 
passages  through  which  the   tidal   v,rter  hr.s  been  rllowed  ingress   and   egress  were 
closed  and   the  water  pumped  out,   The    dam  proved  to    be  perfectly  tight  aid    satis- 
factory in  every  way.   Some   laitance  kad  settled  rt  the   central    depression  as  well 
as  at  a    few  other  points,  and  while   there  were  a   few  spots   of  soft  material  the 
mass  of  concrete   on   the   whole  was   found   to    be  of  excellent   character  and  the 
remainder  of  the  pier  was  built  upon  it  within  the  coffer  dam  in  the  dry.  After 
the  completion  of   the  masonry   the  upper  portion  of  the  dam  was  removed  do  van   to 
ar_  elevrtion  a  little    below  mean  low  water;    its   lower  portions  were  allowed,  to 
re.r.ain  in  place,  serving    to  protect  the   footing  courses  of  the  pier.   One   of  the 
dangers  to   be  guarded  against   in   the    construction  of  such  a  foundation  is   the 
possible  v.rshing  of   tie    lower  portion  of  the  concrete  by  rny  cm  rent  -which  may 
find  its  way  und.er  the   dam.  All  points   of  access  should   be  effectually  ard 
absolutely  cut  off,  as  is  done  by  the   coffer  dam  when  completed  in  the  proper,  man  - 

ne  r  , 

The  plan,  T?ig.59,   shows  the  main  features   of   the  construction  of  the 

pier  above   the  concrete   footing.  There   are  seen  to  Th>e  two  concentric  tiers   of  the 
dressed  stone,   the   outer  one   forming   the    face  masonry.   The  her  rt  ing  is  that  part 
of  the  pier   inside  of  the   two  tiers   of  dressed  stone   end    is   of  concrete  Ko.   5> 
which  in  this   case  means   1   cement,   5    sand  ard   5  broken    stone.   The  material   is   dis- 
tributed  in  this   irr.nner   for  the  reason   that    the  track   on  too  of  the   pier  which 
carries  the    entire   weight  of  the    superstructure  of  the    draw  span  would  rest   im- 
mediately over  the   concentric  tiers   of  dresr-ed  stone.    The   hearting   of  concrete 
ivios.   3  carries   very  little    load  and   consequently  .lay  be   less  ric,h  in  csaent  than 
that  used  in  the   footing  course.   The  central  block  of  concrete  too.    2,   I  cement, 


190 

2  sand  and  4  broken  stone  ,    carries  the  pedestal  block   (shown  on   the   plan)  which 
supports  the   heavy  central  casting  about  which  the    superstructure    turns.     The 
4  inch  pipe  which  is   shown   ranning   from  the  central  portion  of  the  upper  surfcce 
down  through  the  masonry  to  a  point    outside  drains   the  top  of  the  pier  after  the 
track  of  the  draw  span  is  in  place.   In  present  day  practice   it   is  not  uncommon 
to  build  the  pier     entirely  of  concrete,   Ashlar  face   stones  are  now  used  mainly 
for  appearance. 

The  anchor  bolts  which  hold  the    center  casting  in  place  on  the   top  of 
the  pedestal  block  run  down  into  the   concrete   about  4   ft.    These   bolts  are  frcm 
1  1/2  to   2  1/2   ins.    in  dirrn.  and  may  be  built  in  the  masonry  with  proper  anchor 
plates  at    their   lower  ends,   or  they  may  have   split   lower  ends  with  w edges  r.nd 
ragged  sides.   They  may  be   8  to    12  in  number  according  to  the   size  of  the   central 
casting.   They  should  nave  sufficient   resistance  to  hold  the  center  casting  rigidly 
in  place  so    that  there   nay  be  absolutely  no  motion  while  the   bridge  is  turned. 

VARIATIONS  OF  THE  COFFER  fi!.M  PROCESS 

Fig.    59  exhibits  a  typicrl    example   of  hervy  coffer   drin  construction   for 
"bridge  pier  work.   Coffer  dams    of  lighter  construction  are   often  used:    see   Figs. 
38  and  39.    These    diagrams   show  pier  construction  for  Karlern  Rifcer  Highway  Bridges, 
Hew  York  City.  These  piers  were  sunk  in  marshes  along  the  itiver  banks  where  the 
ground  water  level  rose  near  to  the  top  of  the   excavr.tion-   The  piers   shown  by 
Bigs.   38  and  39  were  built   about   1895.   During  the  past    two   decades   (1903-1925) 
some  of  the  lighter  coffer    drm  work   has  been   constructed  of  structural   steel   sheet 
piling  rather  than  wood.   Consult  Eng.   wews,  Vol.60,   p. 394,    for  a  description  of 
large  steel    sheet  pile  coffer  drms\for  a  ship  lock  at  Buffalo,  Hew  York.   The   .nasonry 
sea  walls   of  these   locks  were  built   inside  long  lengths   of  sheet  pile  coffer  dams 
subdivided  into  pockets  by  cross  walls'  of  steel    sheet  piling.   Laclcawanna  Inter- 
locking  sheet  piles  were  used;  see   Fig.40,   group  2, 

Any  cylindric  caisson,  whether  of  wood    staves,    as   for  pile  clusters 
under  docks,    fig. 49,   or   of  sheet  steel    shells   when  driven   ir.  river   beds,  employs 
cofier  dam  principle  of  construction  when  the    caisson  or  tube   is   driven,   or 


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191 

water  jetted  to  refusal,   excavated,  pumped  out,  ani   then   filled  with  concrete. 
Sometimes  such  cylinder  using  wood  or  metal  shells  are   first   sunk  by   the   pneu- 
matic process  and  in  early  days  {the  middle  of   the  last  century)  were   sunk  by 
the   so-called  vacuum  process.    Having  reached  their  proper   depths,  the  pneumatic 
cylinders  after  sealing  at  the    cutting  edge  become  coffer  dams   for  the  remainder 
of  the  'work. 

PIVOT  PjER,  SEVENTH  AVE.  SWING  BRIDGE,  NEW  YORK  CITY. 

In  Fig. 65   is  shown  a  pivot  draw  span  pier  for  one   of  the. New  York  City 
bridges.    The  type   of  construct!  or.  in  general  is    somewhat  si  nilar   to    that. of 
Fig.  59.    But  the  structure  while  being  sunk,    instead  of -being  a  coffer   dam,    is    in 
the  first    instance  an  annular  pneumatic   caisson.  After  .reaching  rock  rnd  when  the 
work  ing- chamber   is  sealed  with  concrete,    the  structure  properly  becomes  a  coffer 
dam  shell  -to   be  excavated  in  the  interior  and   filled  with  concrete  and  masonry 
just   like  the  work  of  Fig. 59. 

The   term  "coffer  dam"   is  often  used   for  the  detachable  wood  box  which 
during  construction  fits  upon  the   higher  levels  of  a  deep  pier.   Such  coffer  darns 
are  detachable  timber  box-like    frames  which   extend  usually    from  the  mud   line   or 
river  or  bry  bott  cm  to  above  mean  high  water.    Within  this   box.  the  upper  part  of. 
the  pier,  lighthouse   or  water  intake,   is  built  in  the  dry,    after  which  the  coffer 
dam  is    removed.  Below   the  mud   lire  or  water  bottom  the    foundation   extends  to  rock 
or  other  suitrb'le  foundation   bed,    usually  of  crib  work  construction.   See  Eng. 
^ews,  Vol.37,  p. 331;  also  Fig. 64   for    illustrations  of  these   special  detachable 
coffer   dams.    Consult  also  "The  Design  of  a  Railway  Bridge  Pier"  by  C^Derleth.Jr. 
plate  7.   See  also  Baker,   Treatise  on  Mr.sonry  Construction,   Fig. 93,  p. 434.;   and 
Patton,   Practical  Treatise  on  Foundations, 

DUMBARTON  BRIDGE  FOUNDATIONS. 

The  recent  construction  of  piers  for  the  Dumber  ton  bridge,   San  Francisco 
Bay,  exhibits  a  special  application  of  the   coffer  dam  process,    See  Trans.  An.' 
Soc.  C-E,  ,  Vol.76,  p. 1572.   These  piers  consist  of  steel   shells    filled  with  con- 
crete and   rest   on  pile  clusters.   To  protect  the  piles  r.r£:  piers   against   erosion, 


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192 

the  pile  clusters  extend  upward  into  the   steel    shells,    vhich  are    of  circular 

plan;   the  largest    shell  being  40   ft.   in  diameter;   the  smallest  18   ft.  Because  of 
the  swift  tidal  currents  these    shells  had  to   be  held  in  place  by. a   structural 
steel   framing  very  similar   to   the   framing  of  a  gas  holder.   The    steel   shell  cor- 
responds to   the  gas  holder   tank  but  was  slid  into  place  in   sections   outside  its 
frame;    one   section  of  shell  after   mother  being  added' as  the   work  proceeded  from 
the  bottom  upward.   Concrete  v^.s  deposited  inside  these   shells   in  still  water.    The 
steel  frame  and    first   sections   of  shell  were  weighted  and  jetted  to  piece  after 
about  10   ft.   of  mud  and   sand   tod  been  dredged  frcm  the  pier    site  with  an  orange 
peel  bucket.    For  the   largest  pier    the    frame  and   shell  were  placed  and  the  dredging 
and  pile  driving  done   from  false   vork   built  upon  eight  clusters  of  piles   driven 
to    forma  hollow  square,  48  ft.    on  a  side,    enclosing  tiie  pier  space.   After    the 
first    sections   of  pier   shell  were   in  place  about  their  guide   frame  the  ground 
within  was  further  excavated,   the  center  portion  being  dredged   about  5  ft.    Deeper 
than  at  the   outside  which  just  about  offset   the  uplift  of  ground  due   to   driving 
the  outside  row  of  piles    first  and  working  towards  the   center  with  succeeding 
piles.   Concrete  was  deposited   in  any  section   of   the    shell  to  within  7  ft.    of  its 
top,  this  being  the  highest   level  to  vhich    the  concrete   could  be  placed  with  out 
disturbance   from  the  tidal   currents  passing  over  the  top  of   the   section.  A  bottom 
dump  bucket  was  used  raving  a  capacity  of  18   ca.ft.   A  diver  wcs  continuously 

employed. 

ADPITIOHAL  REFERENCES 

1.  Harlera  Ship  Canal  Bridge;  V/.H.Burr,  Proc.    Inst.   C.E.    of  Gt. Britain, 
Vol.130,   p. 220. 

2.  See  Indices,  Engineering  wev/s,    1890  to  date,  heading  "Coffer  Dams". 

3.  Ordinary  Foundations;   C.E. Fowler 

4.  Proposed  Coffer  Dam    for  Raising  the   Battleship  ;,!aine,   Eng.Eews, 
Vol. 52, p. 520. 

5.  The  Forth  Bridge;   report  by  P.Phillips 

6.  The  Chicago   Ship   Building  Co.'s  New  Dry  Dock;  Eng. Hews, Vol. 34, p. 50 

7.  New  Type  of  Thin  Wall  Coffer  Dam;  Eng.  News-Record  ..Vol.  83,  p.  817,    191S. 


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193 

CHAPTER  10 
OPEN     CAISSONS 

If  an  open  caisson  is   to  be  employed,   the   foundation  bed  must  be  leveled 
with  a  fair   degree  of  accuracy  to  receive   the  caisson  in  its  true  position.    In 
such  cases   it    is  good  procedure  to  build  a  bottomless  box  with  its  lower   edges 
shaped   to    fit  the  river  bed  or  other  bottom  as  closely  as  practicable.  The  sides 
of  this  bottomless  box  should  be  carried  up  well  tov/nrd  the  surfr.ce  of.  the  water 
or  perhaps  completely  to  that   surface,   so  that 'all  current   at   the  botton  of  the 
box  may  be  entirely  destroyed.  After   the   box  has  beer,   sunk  by  loading  upon  plat- 
forms at  its  top  stone  or   other  heavy  material,' the   open  places  under   its  lower 
edges  must  be   closed.   This   can  be  done   very  satisfactorily  by  depositing  bags  of 
concrete  around  the  interior  of  the  box  and  either  bags  of  concrete  or  bags  of 
sand  around   the  exterior  edges.  A  bank  of    -gravel  or  rip  rap  of   suitable    size,  or 
a  combination  of  th.3    two,   should  be  deposited  about    ube   outside  of  the  box;    the 
latter  in  the  meantime  being  held   securely  in  position  by  such  platforms,   cribs, 
anchors   or  piling  as  the  current  may  rake  necessary.   The   bottom  of  the   enclosure 
thus    formed  must  then  be  cleaned  most  crrofully  and  thoroughly  of  all   clay,   nad, 
sand   or   other  fine  or  soft  material  or  denri^,  by  dredging,  scraping  or  similar 
methods,    in  vjhich  operations  divars  are   frequently  employee:.    This  cleaning  is 
imperative   for  a  good  bond  between  t  he   foundation  bed  and  the    footing   course. 
Concrete  may  then  be  deposited  under  water   frcn  properly  designed  buckets  in    the 
inside   of  the  box  on  the  prepared  foundation  "bed.    'The  upper  surface  of  this  con- 
crete footing  should  be  truly  horizontal    raid  usurlly  the  aass  need  not  be  more 
than  two  to   three  feet   in   depth  at   its   shallowest  point.    The  upper   surface  of  the 
concrete  can  be  mr.de  horizontal  v.hen  it   is    being  deposited  by  placing  either   small 
scantlings   of  timber  or  light  railroad  rails  horizontally  across  the    box  along 
its  narrowest  dimensions  so  that  upper  SIT  faces  may  be  2  to  3    ft.   above  the 
highest  point  of  the   bottom.    The  concrete      should  be  deposited  in  uniform  layers 
until  the  too  of  the    freshly  deposited  mass  is  a  little  above  the  upper    surfaces 


';.    ~ 


194 
of  the    scant  lings  or   mils;    tfce   letter  being  6  to   8  ft.    apart.    If  a  lighter 

railroad  rail  or  other   similar  bar  of  metal  be   swept   along   the    tops  of  the   scant- 
lings the  upper  projections   of  the    concrete   will  b  e  smoothly  leveled  off  and 
most  or  all   of   the   depressions  in  it  will  be    filled.    If  any  depressions  wfcicfc  «re 
not  filled  be    found,   additional   concrete   can  be   deposited  at   such  points  whether 
before  or  after  the.  leveling  rr.il   is   swept   over   it.    In  using   this  leveling  rr.il, 
particular  care  should  be  taken  to  disturb   the   concrete   only  so   much  as  may  be 
necessary  to   level   it. 

The  concrete    footing  mass  will  thus  be  located  at    the  bottom  of  a  well 
of  absolutely  still  water  and  it   should    be  allowed  to   set  from  2  tor  3  to  4  or  5 
weeks  before  a  load  is  placed  upon  it.  At  the  end  of  that  period  of  time  it  should 
be  carefully  tested  by   the   end  of  an  iron  rod  or  pipe  at  all  points  of  its   surface 
to   discover  whether   it  has  hardened  in  a   satisfactory  manner.   If  it  has  not,  all 
soft  portions   should  be  carefully  excavated,  by  a  diver   if  necessary,   and   the 
resulting  depressions    filled  with  rich  mo  roar    or  concrete   in  suitably  sized  bags 
so  that  a  satisfactorily  hard,    continuous   bed  may  be  afforded  for  the  reception 
of  the   open  caisson.   This  type  of  bottomless  box  is  shown    in  Fig. 60.    The  sides 
are  seen  extending  up  to  mean  low  water  and  down  to  the   rock  bottom  enclosing  the 
mass  of  concrete  3   ft.  thick-.   For   a  distance  of  6  ft.    from  the  bottom         the 
sides  of  the  box  are  made  of  4  in.  by  12  in.   planks,   and  above  that  elevation  of 
2  in.  planks.  The   vertical  pieces  to  which  the  plank  sides  are    bolted  or  spiked 
are  4   in.   by  8   in.    in  section  and  about  4   ft.    rprrt, 

PIER   III,   KkRLEM  SHI?  CA1&L   BRIDGE,   ME7  YORK. 

•   ThS  open  caisson  shown  in  both  horizontal  an?,   vertical   section  in  Fig. 60 
•was  built  on  two  layers   of  12  in.   by  12  in.    timbers  laid  solidly  at  right  angles 
to  each  other,  with  a  6  in.   by  12  in.   caulked  platform  above  them.   This   solid 
timber  bottom  is  built  either  on  shore  and   launched  or  else    in   the  water.    The 
6  in.   by  12  in.  plank  sides   are  then  built  around   the    edges   of  this  solid  timber 
platform,  but  ore  not  bolted  or    spiked  to  it.. Those    sides   are  simply  held  down 
on   the   platform  by   the    1   1/2    in,    rods  running   from  the    10  in.   by  10   in. 


195 

cap  pieces  down  to   the  upper   layer   of  12  in.   by  12   in.   sticks.   Horizontal   recesses 
are   cut  into  the   latter   timber  in  which  butts   for  the  rods   are  placed.    The  rods 
may  therefore  be  entered  in  the  holes  provided   for  them  and   screwed  in   the  nuts, 

* 

thus  giving  them  a    firm  hold  to    the  bottom  of  the  caisson.   When  the  upper  nuts 
are  screwed  down  onto   the    cr.p  piece   the    sides   of  the   caisson  are  drawn  so  tight 
on   the  caulked  platform  that   the   joint  between   the    sides  and  bottom  of  the  caisson 
may  be  made  water   tight.  Eye-bolts  and  hooks  are  sometimes  used  to  hold  the  sides 
of  the   caisson  in  place  and   other  devices  are  also  employed.  After  the  caisson  is 
thus  constructed  either  partially  or  wholly,  One  side  of  the  bottomless  box  already 
described  is  removed  down  far  enough   to  permit   the   open  caisson  to  be  floated 
into  place  immediately  over  the  concrete   bottom.   The  masonry  of  the  pier   is  then 
started  on  the  caulked  platform  of  the   caisson,   the   whole  gradually   sinking  as 
the  masonry  is   laid  in  place.    V/hile  this    sinking  is/progressing,   the   caisson  must 
of  course   be  held  rigidly  in  its  proper  position  by  requisite  platforms  and  braces 
so    that  when  the  sinking  is  completed  it   shall  rest  accurately  on  the  concrete 
bed.   If  water  leaks    into    the   caisson  to  any  material   extent,   it  must  be  pumped 
out.  As  the  caisson  sinks,    its  sides  are  braced  either  against   the  completed 
masonry  or  against  each  other,   so    as  to  resist   the   increasing  lateral  pressure 
of  the  water. 

A  reference  to  Fig. 60  which  represents  the  bottomless  box  and  caisson 
actually  used  in   the  construction  of  the  Harlem  Ship  Canal  Bridge,   New  York 
City,  will  make  clear  the   various   steps  of  tiiis    process  of  pier  building  as  well 
as  the  methods   of   framing  ard    the   dimensions   of  timber   suitable    for  the  Con- 
struction. After  the  pier  is  completed,    the  nuts  on  the  upper   ends  of  the    rods 
holding  the  sides   of  the   caisson  in  place  are   loosened  and  the  rods  themselves 
are  unscrewed  from  the  nuts  in  the  upper  layer  of  platform  timbers.   These  oper- 
ations release   the   sides  of  the   caisson  and  allow  them  to   be  removed.  The   sides 
of  the  bottomless  box  are  then  cut   off  or  otherwise   removed  down  to  or   below 
mean  low  water.   The  remainder    of  the  box  is   frequently  left  in  place. 

If  the   construction   is  in    sea  water  so   that  marine  borers  may  destroy 


.•-•••.  1 .-    -•:•••:, 


;v     ".:   '1  , 


196 

he    timber,   it  will   be  best  to  deposit  more  gravel  or   rip  rap  or  both  around 
the  bottom  of  the  pier  until  the  timber  of  the  permanent  part  of  the    fbunlation 
is   covered,  as  those  animals  work  only  in  water.  As   the  plans    show,   there  must 
be  a  minimum  clearance  betv/een   the  caisson  and  the   enclosed  masonry  of  a  foot 
to  18  ins.  at  the  bottom  of  the  pier. 

OPEN  CAISSON  SUPPORTED  ON   Hjg_S 

The   same  aethod  of  build  ire  a.  pier  within  an  open  caisson  is  also  fre- 
quently employed  where  the  bottom  is   soft  enough   to  permit    the  use   of  piles. See 
Fig.GOA.  Under   such  circumstances  piles  are  driven  in  as   regular  order  as  pos- 
sible  over   the  entire   foundation  site,  with  centers   rbout  3  ft.    apart.    The  piles 
are  cut  off  at  such  distance   below  mean  low  water  as  will  insure  all  timber  be- 
ing always  under  water  or  at   least  saturated.  The  machine  for  cutting  off  the 
piles  under  water  consists    simply  of  a   vertical  shaft   fitted  with  a  pulley  and 
frequently  held  between  the    leads   of  a  pile   driver  v.'ith  a  circular  saw  attached 
to   its   lower  end.  The  pulley  on  the    vertical  shaft  is    belted  back  to  and  rotated 
by  an  engine  on  the    scow,  after  the   saw  is   set   at   the  proper  elevation,    it  is 
put  in  motion  and  moved  about  so  as   to   cut  off  all  the  piles  at  a  uniform  ele- 
vation.   In  tidal  waters  the   elevation  of   fee    saw  must  be  adjusted  to    the   varying 
stages   of  the    tide.    The  open  caisson  constructed  as  already  described  is  then 
floated  into  place   over  the  pile    foundation  and  properly  braced  and  gilded  as 
it   sinks.    The   construction  of  the  masonry   within   the   caisson  causes    it    to   sink 
gradually  until  it   rests  as  nearly  •un±--~r>£mly  as  possible  on   tha    tops  of  the 
piles,    instead  of  on  the  concrete   foundation  bed   in   tlie  previous   instance. 

Before  the    caisson   is  brought   into  position  over    the  piles  the   latter 
should  be  carefully   inspected  or    tested  so  as  to   determine  v.hebhe~  the   tops  are 
all  at  the  same  elevation.    If  the  piles  Ir.ve  not  been  truly  cut   of f  a*   en* 
elevation,    it  nay  be  feasible   and   satisfactory  to  place  on  the    tops    of  t^ose 
that  are  low  partially  filled     bags  of  corcrete.   Or,  as  is    sornetirne.-;  C  one .   v.l.in 

t.  - 

mattresses  of  corcrete  may  be  placed  on  the  tops  of^ number  or  all  ol  tl:o  pilss, 


.    •- 


if  the    caisson  or    other   imposed  load  can  be   brought  do\vn  on  the  concrete  before 
the    latter  is   set.    The    imposition  of  heavy   loads  upon   fresh  concrete  thus   placed 
v.lll  compress   it  over  the   tops  of  the  piles  to   such   extent  at  each  point  as  the 
depressed  elevation  of  the   top  of  the   pile  may  reouire.  This  method   of  leveling 
the  tops  of  piles  that  are  irregularly  cut  off,   if  performed  with  due  cr.re  .and 
judgment,  v.'ill  be  productive  of  satisfactory  results,      Obviously  the  method 
is   ruite  impracticable    if  the   load  cannot  be  imposed  before  the  concrete    is    set, 

In  all   these   cases   of  gradual  sinkirg  of  a   caisson  by  the  increasing 
.'nr.ss  of  ;^r.sonry  v/ithin  it,    careful  computations  should  be  made  to  determine 
v/hr.t  the  depth  of  submersion  will  be  at  different  stages  of  the  work.    This  in- 
formation is   needed  for  the    sr.fe  regulation  and  control  of  the   sinking  caisson 
and   its  load.    In  all  cases  the    sides  of    the  caisson  must  have  joints  caulked 

ith  oakum  or  other    similar  nrterial,  preferably  from   the   outside,    in  order 
that    the   enclosure  may 'be  as  nearly  xr.ter  tight   as  possible. 

This  method  of  founding  piers  is   very   economical  \vherever' it  may  be 
applied.    It  is  not  adapted  to   great    depths  of  water  although  its  rair;e  of 
application   is  sufficiently  v/ide  to  include  :viany  structures 

ADDITI  Qli'. L  REFERENCES 

1.  Caisson  Used   in  Founding  the  Swr.  \Vall  at  San  Francisco,  by 
Randall  Hunt;  Eng.  Hev/s,  Vol.24,   p. 96. 

2.  Reinforced  Concrete  Caissons,   Their  Development  and  Use    for  Break - 
V/aters,  Piers  and  Revetments;  by  W.y,Judson.,  Eng.  Lev/s,Vol.62,p.34 ;  Western 
Society  of  Engineers,  Hay  19,   1909. 


198 
CHAPTER  U 

PNEUMATIC  CAISSONS 

A  pneumatic  caisson  is   a  box  or   compartment  opening  downward.   Its  side 
and  top  ere  sealed  to  prevent   escape  either  of  r.ir   or  water.    The  box  is  sunk  or 
made  to  penetrate  in  water  or  water-bearing  /naterials.  During  the  process  of  sink- 
ing water  is  expelled  or  displaced   from  the   box  or  caisson  chamber  by  means   of 
compressed  air.  This  enables  men  to   30  into  the  chrmber    to  excavate  material  under 
the  cutting  edges  or    in  other  v:ays   facilitate   the  removal   of  -naterial  and  sinking 
of  the   structure . 

The    foundation  proper   is   bailt  immediately  upon  the  working  chrmber, For 
.r.rge  and  deep  piers  the    foundation  produces  its   own  necessary  sinking  weight. 
Mrcller  caissons  such  as  are  used  under  buildings  must   often  be  additionally 
weighted  xvith  pig  iron  or   .rcsonry. 

For  the  passage  of  men  and    viaterials  vertical  shafts  extend    from  the 
caisson  roof  to  elevations   above  the   permanent  water  level.    Somewhere   in  each 
shaft  there  is  an  air   lock.   In  modern  work  the   air   lock  is   always  at  the   top  of 
s:aft  above   the  permanent  water  level. 

The  caisson  men   (often  termed  "sand  hogs")     dig  out   the  material  viiich 

• 

consists  generally  of  mud,   srnd,    .gravel,    loose    stories,   boulders  and  the   like, They 
dig  especially  from  under  the   cutting  edges.   Blasting   is  someti:nes  resortsd  to. 
Specially  designed  buckets,   mud  and  srnd  pumps,  and   other   excavating  machinery   are 
frequently  used  to   lift   the  major  part  of  the    vr.terial  which  is    token  out' through 
the  material   shafts   or  by  pipes,    is  dumped  into    scows  ani  carried  av.r.y. 

As  the  excavation  proceeds  the   caisson  and   structure  above   it   gradually 
sink  until  the  cutting  edges  reach  bedrock   or  other  suitable    foundation  stratum. 

~ 

The  deeper   the    foundation  .bed  below  the  water   surface  the  hi^ier  must  be  the 
air  pressure  in  the  caisson.    The  grerter   the   air  pressure    the  more    serious  is   the 
inconvenience  ard   finally   the  danger  to  the   workmen.  Thus,   the  process  cannot  be 
used  for  depths   grer  ter    'ohan   about  120  ft,   "below  water  surface.    Indeed,    for   depths 
greater  than  100  ft.    the  most    important    problem  is   the   care  and   handling  of  the  met 


1   . 


199 

At  this  place  a  general  comment  mi;;ht  be  made  as   to  the   fitness  of 
different  processes   for  driving  -.piers  to    depths  below  vr.ter, 

The   processes  describee!  in     Chapters  9  to  12  inclusive  usur.lly  may  carry 
structures  to    the    following  depths: 

Coffer  dam  40  ft.    to  45  ft. 

Open  Caisson  40  ft. -to  45   ft. 

Pneumatic  100  ft.    to   120  ft. 

Deep  well    dredging  175  ft.    to   200   ft. 

HISTORY  OF  THE  PKEUMATIC  PROCESS 

The    ider.  and   possibilities   of  this  process  h-ve  long   been  known  to  engin- 
eers.   The    first  conception  dates   from  1647.    In  1779  Coulomb  presented   to   the 
Paris  Acr.demy  of  Science  r.  prper   explaining  hov:  to  execute  excavations  under   wa'ie*1, 
His  proposed  apprratus  was   very  similar    to   that   now  in  general  use. 

Two  processes   for  utilizing  a  difference  of  air  pressure   for    sinking 

* 

foundrtions   under  water  /x-y  be  recognized: 

1.  The  Vacuum  prccess 

2.  The  Plenum  "xrcoess 

a.  the   pneumatic  pile 

b.  the  pneumatic  caisson 

Pj^yijmc  PILES. 

The   earliest  piles  sunk   either  lay  the  vacuum  or  plenum  processes  were   of 
.-natal;  either  wrought   or  erst  iron.    Such  cylinders  were  usually  composed  of 
sections   from  6  to    10  ft.    long  and  2  to  8    ft.    in  diameter,  bolted  togetJuer  by  in- 
side  flanges;    see  Baker,  Art.    863,  p. 429,   ed.    1909. 

VACUUM  PROCESS 

The  vacuum  process  consists  in  exhausting  the   air    from  a  caisson   (usually 
cylindric   in  form)    from  which  cylinder   the   .material  hrs  been  considerably  excavated 
so   that   the  air  pressure   from  without  acting  on  the    cylinder  top  mr.y    force   the 
structure  downward     By  exhausting   the  air  within    the   pile,   water  flows  into  the 
working  chrmber,  under  the  cutting  edge,  thus  loosening  the  soil  and  causing  the 
cylinder  to  sink.    The  process  has   only   been  used    for  piles  sunk  through  mud  or 
sard.   The   method   is  now  obsolete.   The  vacuum  should  be   obtained  suddenly  so  that 


.  t 


200 
the  atmospheric  pressure  may  give  the  effect  of  a.  blow.   Cylinders  hr.ve  bean 

sunk  by  this  method  5  or  6   ft.  by  r.  single  exhaustion.   See  firmer,  Art. 859 , p. 428. 

PLENII!  PROCESS 

/ 

The  plenum  process   in  3  ts  ma:n   fertures  has  already  been  described  in 
the  introductory  paragraphs  of  this  chr.pter.    It  cr.n  be  applied  in  sinking  foun- 
dations through  all   clr.sses   of  soils.  The  smaller  cr.issons  in  form  are  pneumatic 
piles  about  6  to  8   ft.    in  diameter,  s  imilatr  in  general  appearance  to  those    tlrt 
were  used  in  early  days   for   the  vacuum  process,  it  present  they  are  common   for 
building  foundations  or   for  small  bridge  piers.  They  may  be  of  structural  steel 
or  of  wood   stave  construction.   See  references   to   Building  Foundations;  particularly 
Ens.  Kews,   Vol.40, p. 363,   for  wood  caissons;  and  En*>  News,  Vol.30 , p.  458,   for 
metal  designs.   Lately   sane   caissons  nave  been  built   in  part  or   vhole  of  reinforced 
concrete,  see  Eng.  Record,  Vol.62,  p. 556. 

Pneumatic  caissons  of  large  sizes  are  generally  rectangular  or  polygonal 
in  plan.  Most  building  caissons  where  not  circular  are  rectangular,    of   sizes  about 
8   ft.    by  16  ft.   to    12   fit.   by  24   ft.      Sometimes,   as    for  pivot  piers,    caissons   are 
polygonal  and.  annular,  Fig.   65.   The  great  Forth  Bridge  caissons   are  circular   in 
plan,   Fig. 66;   those   of  the   St.    Louis    bridge  are   irregular  hexagons.    Both  the  Forth 
and  St.   Louis  caissons  are   steel.   In  the   last  thirty  years  fc/e  greater  number  of 
large  caissons  sunk  for  bridge  pier  work  hr.ve  been  of  v/ood  construction,   see 
Fig. 64;  also  Eng.  iiews.Vol.  65,  p. 320;   Vol.61,  p. 63;  •  Vol.63,  p. 9;   Vol.62  , p.  546, 
In  the   last  ten  years  many  caissons,   particularly   snail  ones  for  buildings,    which 
formerly  might  have  been  constnucted  of  wood,  are  nov/  being  built  of  structural 
steel   or  of  a  combination  of  wood   and  steel,    or    even  of  reinforced  concrete. 

Wood   cais.sons    like   Fig. 64  will  never   be  altogether  superceded  by  struct- 
ural steel  designs  or  by  reinforced  concrete.    The  selection  of  type   is  mainly  a 
matter  of  dead  weight,   V/here  great   piers  are  sunk  to  depths  below  water   level,    as 
in  the  case  of  the  Memphis  Bridge,  anc.  rest  upon  sand,  clay  or  hardpan  at  depths 
of  90  to  100  ft.,   safe  abnormal  pressures  must  not  be  exceeded.    Therefore   the 
pier  must  have  considerable  plan  and    relrtively  light  weight  per  cu.    ft.    of  volume. 


. 


201 
This  condition  cannot  be   obtained  through  the  design  of  a  structural    steel 

caisson  filled  with  concrete,  whose  weight  must   obviously  be  not  less  than  150 
Ib.  per  cu.ft.  On  the  other  hand  a  caisson  half  of  whose   volurre   or  more  is  timber 
and  the  rest  concrete  ani  metal  can  have  a  dead  weight  averaging  100  Ib.  per  cu. 
ft.    or   less. 

The  greatest   developments  in  caisson  work  have  been  made  recently  (1) 
•  in  the  care  with  which  the  vorkraen  are  treated,    (2)   in  the   design  of  men  and 
material  shafts,  and  (3)    in  the   construction  and  operation  of  air  locks.    In  the 
Brooklyn  Bridge  caissons,   Fig.67,    the  two  material    shafts,    7   ft.    in  diameter., 
which  -project  downward  through  the    caisson  roof,  during  the  sinking,  were  sealed 
at  the  bottom  by  a  water  trap.   Such  designs  offer   great  danger   fran  possible 
blow-outs.    In  the   same   pier  the  iir.n  shafts  were  3  ft.   6   in.   in  diameter   with 
air   locks  7   ft.   high  by  6  ft.    6  in.    in  diameter,    situated  just  above  the    caisson 
roof.   In  modern  work  both  types   of  sha ft  would   be  condemned;   the  material  shafts 
because  of  the  danger  from  blow-outs;   the  men  shafts  because  the   air  locks  are 
far  below  the  outer  water  level;   3D    that  in  case   of  accident  men  could  not  reach 
srfety  but  would  be  drowned. 

"The    first   foundations  sunk  entirely  by  modern  compressed  air  prxesses 
were   the  pneumatic  piles    for  a   bridge  at  Rochester,   England,  put  down1  in  1Q51; 
the  cutting  edgt  reached  a  depth  of  61   ft.   The   first  pneumatic   caisson  proper  was 
employed  about  1870  at  Kehl,  France,   for  a  railroad  bridge   across  the  Rhine,    The 
first  three  pneumatic  pile  foundations  in  America  were_  constructed  in  South 
Carolina  in  1856-60.    The   great   St.    LOUJ,S  bridge  caissons  were  put  down  in  1870 
to  depths   of  109  ft.    8  1/2  ins.,  which  depths  have  hardly  been  exceeded  since". 
Cf.    Baker,  Mrsonry  Construction,  ed.    1909,  pp.  428-455. 

CAISSON  DESIGN  AND  OPERATION 

The  clear  height   within  the  working  chrmber   should   be    from  7  ft.   6   in. 
to  9   ft.,   so    that   the  men  may  have  sufficient  head  roan  for  their  work,   but  no 
ercess.    The  roof  of  the   caisson  must  be  able   to   hold  at   lenst  all  that  part  of  the 
structure  above    it  necessary   to  produce   the    sinking  weight,  neglecting  the  upward 


~>       .». 
-•.         .,./    V 


'•,'•--• 
•   ;  •-'•     V          ';..       •- 

V:C    ":'r--  ^^    -O;;-       - 

•       "  '•  ~ 


i^.;- 


.    :' 


202 

air  pressure  in  the  caisson  since  at  r.ny  time  a  blow-out  may  occur.  After  the 
foundation  is   completed  the  caisson  chamber  is   filled  v/ith  concrete   and   the   roof 
rio  longer  must  support  a  part   of  the  s  inking   weight  as   a  beam.    The  working  stresses 
in   the    roof  material  can  therefore  be  taken  high,    especially   for  steel  caissons. 
The    side  plates  or  walls  of  the    caisson  carry   considerable    of  the    si  nk  ing  weight 
to  the  cutting   edges  and   also  ;.iust  withstand  the   lateral  pressure    from  the  material 
without.  Brackets  and  stiff eners  reinforce  these   sides  to  properly  carry  the 
weights   from  the   roof  to  th".  cutting  edge.  Again,    brackets  and   stiffening  beams 
or   trusses,  running  horizontally  between   the   brackets,   and   vertical   struts,  must 
ireinforce  the  sides   from  being   forced  i invar d.   V.'ith  .great   depths  the  pressure    from 
without  upon   the   sides  maybe  enormous,    especially  if   Icrge  boulders   are  encounter- 
ed,  did  glanced  by  the  cutting   edges.    Too  -great  a  precaution  cannot  be  taken  with 
this  part  of  the  design.  These   stresses  also  are  temporary   and  vanish  with  the 
completion  of   the  work. 

The  caisson  chamber  must   be  thoroughly  caulked  whether  of  wood  or  iron 
to  prevent   Irrge  losses  of   compressed  rir.   The  men  shafts  should  be   so  located 
anc:  b  e   of  such  numbers  that  in  case  of  accident  the  workmen  may  readily  get  to 
them.   For  safety  the  air  locks   should   be  high  up   in  the    shafts.  The  material  shafts 
should  be  so  Disposed  that  the  excavated  caisson  materials  need  not    be  handled 
and  carried  too  much  in  the  v.orking  chambers.   Therefore    for  caissons  of  large 
plan  it    is    economy  to  have  a  number  of  material    shafts.  The   tops  of   the  man  shafts 
should  always    be  above  v/ater    to   avoid   accidents  to  the  workmen   bolow,    should  the 
coffer  dam  give  way.   The  material   shafts   need  not   necessarily  but  preferably 
should  rise  above  water.  All  shafts  are  made   in  cylindrical  sections  bolted  to- 
gether through  external   flanges  between  which  rubber  bands   or  sane   soft  ar.d  im- 
pervious substance   is  placed   to  render  the  joints  air   tight.    The  men  shafts  are 
usually  3   ft .    6  in.    in   internal  diameter;    the  material    shafts  about  3  ft.;   just 
sufficient   to   give  clearance  to   the    buckets.   Buckets  are  usually  cylindrical, 

about   2  ft.    6  in.    base  diameter,  and   3  ft.    to  4    ft.    high.  Air   locks   for  men  are 
usually  4   ft.   6    in.  by  7   ft.   high   with  ordinary  hinged  doois  at   top  and   bottom. 


.T     ' 


203 

Air   locks  for  material   shafts  are  of  patented  types,   or   sized  sufficient  to  pass 

'    .  • 

the  buckets,  with  hinged  doors  below  and   with  sliding  doors  above,  generally 
operated  by  compressed  air.    The    sliding  doorshust  be  designed  to   allow  the   buckets' 
steel   cable    to  pass    through  them  without    excessive   loss  of  compressed  a  ir,  All 
locks  should  be  at  the    shaft   tops.  As  the    structure   sinks,    additional    sections 
are    bolted  to  the    shafts,   first  removing  and  then  again  replacing  the   locks. After 
rock  bottom  is  reached  and  the   caisson  is   filled  with  concrete  as  much  of  the 
shafts   as  possible  should   be   removed  for   future  use   in  other  work.  Air  locks   are 
always  removed, 

Sinking  '.'/eight.   The  normal  frictional  resistance  on  the   sides   of  pneumatic 
caissons  varies  with   the    depth  ard   is  usually  found   between  300  and   600  Ib.  per 
sq.    ft.    for   depths    of  50  to  90  ft.    in  sand,  silt  and1,   mud;    see  Chapter  2,  p. 48. 
When  boulders  are   encountered  the    resistance   is   greater.    When  much  air  escapes 
under  the   cutting  edges   the  resistance  is    less.    The   head  of  water  outside   of  and 
the  compressed  air   pressure 'i thin  the  caisson  produce,    especially  with  great 
depths ,  a   considerable  buoyant  force  v/hich  can  be   rerdily  con  pa  tec"..    The   sinking 
weight  at  all  stages  of  the  work  must  be  sufficient  to  overcome  these   resistant 
forces   of  side    friction  and  buoyancy  together  with   the  direct  resistance  at   the 
cutting  edge.  KJ::.'.  •.-.   caisson  is  excavated  under   cutting  edges  and   ready    for  the 
next  stage  in  the  sinking,  a  sudden  exhaustion   of  air   gives  the   effect  of  a  blow 
to  start  the  mass  of  the   foundation  downward. 

Caisson  Flotation.  Caissons   rre  usually  built   upon  the   shorfc,   then  launch- 
ed and  towed  to   the    foundation  site,  where  they  are  accurately  located,   held   in 
position  by  cables,    staging  and   piles,   and    the  work  of  sinking  commenced.    It  is 
imperative  therefore    so    to    design  the    caisson  and   such  pr.rts  of  the  crib  or 
coffer  drm  immediately  above  it  that  when  launched  the   structure    shr.ll  have  a 
stable  flotation, 

S  ink  i ng  C  a  i  s  s  on  s .  No  caisson  should  be  allowed  'to  sink  until  a   careful 

examination  is  .rr.de   to  see   that  everything  is  raacVy.  After  excavations  have  been 
..ir.de  under   all  parts   of   the    cutting    ec.ge,   the  men   should  be  brought  out   of  the 


204 
caisson  befcre   sinking  is  begun.    The  power  plmt  should  have  ample  capacity, 

especially  reserve  compressors  to  supply  in  case   of  emergency  large  quantities  of 
air  at  a  moment '  s 'no  ti  ce.    Great    care  must  be   taken  aid   judgment   exercised   in 
sinking  caissons   to   bring  them  into  or  keep  them   in  perfect  alignment.   The  cutting 
edge  is  a  very  important  feature.    It   should  be  made  strong  enough  either   to  cut 
through  an  obstruction  or  lodge  upon  it.   Should  the    edge  fail,   it  may  force   the 
caisson  out  of  position  and  even  ruin  the  v:ork.    In  bringing  caissons  into  align- 
ment similar  principles  of  excavation  are    to   be  observed  to    those  described  later 
for  the   deep  well  process.    In  pneumatic  work    this    feature  of  excavation  can  be 
more   intelligently  and  certainly  prosecuted.   Consult  Eng.  toews  ,Vol.  63, p. 9,    for  a 
description   of  the    sinking  of  the  caissons   for   the  I/lcKinley  Bridge,  St.    Louis. 
The  same   subject    is  treated  further  in  Engineering-Contracting,  Vol. 33, p. 77, 

Excavating;  Lifts  and  Pumps.   Sard   lifts,  mud  pumps,   etc.    operated  by  com- 
pressed air   and  water  are  very  efficient  in  caissons   sunk  through  soft  materials. 
Sea  the  references  in   this   chapter,  but  parti cularly  the  Reports  of  the  Memphis 
and  St.    Louis  Bridges,  ard  the   article  describing  the  Havre   de  Grace  Bridge 
Caissons,  where   different   styles   of  pumps  are   exhibited. 

Physio lo  icr.l  Effects  _of  Conroressed  Ai-.?L''£>I.(L2?±LiL°ILs_  AIL  Krnd li iy*  \7oitemen. 
To  avoid  as  much  rs  possible  the  ill  effects  of  the  pneumrtic  process  on  men  when 
working  at  great  depths,  observe  the  following: 

1.  Select    only  healthy  men 

2.  Prevent    sudd on   changes  of  t  anperature 

3.  Avoid  candles  and   gas,  and  use  only   incandescent   electric  lamps. 
Th&s  prevents  soot   in   the  working  chamber  ,  w hi  ch  men  would  otherwise  breathe   into 
their  lungs. 

4.  In  winter  give   shelter  to   the  men  when  coming  frcm   the  caisson.  Under 
high  pressures  they   should  bo  released   frcm  the   air  locks  with  precaution  so  that 
they  are   not  subject  to  chill    from  sudden  change  in  tenperature. 

5.  See  that  the  men  do  not  indulge  in  alcoholic    .Liquor   or  violent    exercise, 

6.  Rigorously  police    sanitary  rules  in   large  e.aiasors  employing  many  men, 

7.  Shorten   the  working  hours  with  greater    depths,   usi  rg  as   lev.'   as  two 
hour  shifts  for  hinh  heads   of  water  pressure. 

8.  For   great    depths  provide  elevators   in  the  men  shafts. 

9.  In   summer  and  with  great  depths   the  a  is  son1  temperature  is  apt  to  be 
high;   proper  refrigeration   or  cooling  plant   should  be  installed. 

10.   The  air  compressors    :iust  be  able  to    supply  the  rnar'i^urn  quantity  of  rir 
required  per  minute  in   the   crisson,   and  in  addition  that  required  for  emergency 
ard  that   for    the  operation  of  machines  and  to  supply   leakage. Otherwise   there   is 
danger  from  blowouts  rnd    fro,n  sudden  chilling  to  the  men   in  the  chamber. 


205 
For  a  more  detailed  discussion  of  this   subject  read    fee    following: 

1.  French  Government  Regulations    for  iVork  tinder  Compressed  Air;   Eng.News, 
Vol. 62, p. 718 

2.  Caisson  Disease  and    its  Prevention;  by  H.Japp,   Trans.  Am.   Soc.C,!!. 
Vol.65,   p.    1, 

3.  A  Symposium  on  Caisson  Disease,   Eng.   Kews,   Vol.68,p.862. 

4.  Caisson  Sickness,  by  Leonard  Hill,  published,  by  Longmans, Green  &  Co. 
1912, 

5.  A  Compressed  Air  Hospital;   Eng.   News, Vol. 23,   p. 557, 

CAISSON  CONCRETE 

Caisson  concrete  should  be  ric  h  and.  fairly  wet.  Compressed  air  tends  to 
drive    the  water  out  of  concrete.   The  best  Portland   cement  should  be  used;  a   concrete 
of  1  part  cement,  2  parts  sand,  and  4  parts   broken  stone   to  pass  a  one   inch  ring 
is  now  commonly  prescribed.    In  fact  broken    stone    to  pass  a   1/2  or  3/4   inch  ring  is 
sometimes  specified.   Care    should  be  taken  in  laying  and  ramming  the   concrete  .near 
the  roof  and   corners  of  the  working  chambers.    In  large  caissons  it  is  often  advis- 
able to  divide  the  working  chambers  by  partitions  into  distinct  compartments.  This 
reduces  the  tendency   for  serious    accidents  during  sinking  but  separates  the  masses 
of  concrete . 

The  Caisson  and  a  considerable  portion  of  the    foundation  above   it  should 
have  vertical  sif.cs     From   the  cutting  edge  to    the   top  of  the   roof  of  large  steel 

S  • 

caissons  the  height  measures  about  12  ft.;   for  v/ooc.  en  caissons   it   is  more,   about 
20   ft.  A  slight  batter,  perhaps   1  in  24 ,  may   exist   in  the  sides   of  the  permanent 
crib  work  above,  but    large  batters  aggravate   the  problem  of  aligimont  and  do  not 
seem  to  reduce  materially  the    side   friction.   The    sides   of  the   caiason  and  crib 
should  be  as  smooth  as  possible  and  with  steel  designs,  all  rivots  should  be 

• 

countersunk' on  the   outside. 

CRIB  WOHK  AIID  £OFFER  DAM   ^ 

Crib  work  between   the   caisson  roof  and  the   river   bottom,    for  bridge  piers 
may  be  constructed  of  hervy   timbers,   the   spaces  between  the  timbers  being   filled 
v.'ith  concrete.    The  crib   ficminj  should  be    designed  to  make  the    concrete  act  as  a 
solid  ,-iass.  L  detcchable  coffer  darn  with  vertical   sides   is    bolted  to  the    crib  work 
and   bracod  laterally  from  within  to  withstrnc1  the   water  pressure  w  ithout. The   joint 


206 
between  the  coffer  dam  and  crib  work  must   bo  water  tight.  A  layer   of  hemp  raid 

cotton  has  r.t  times  been  used  for  this  purpose.   Inside  ihe  dry  coffer  dam  t  he 
masonry  is  built.      Below  water   the  pier  usually  is  entirely  of  concrete,Tabove 
water   it  may  have  a  cut   stone    froing  vi'th  a  concrete  Iierrt.  After  the  pier  or 
structure  is   conplete  above  v/ater  the   coffer  darn  may  be  removed  and  used  again 
some  where  else, 

i  EAST  JIIVEB  3EIDG-E 


Fig.   63  shows  one   of   the   tower  piers  of   Hie  ivew  East  Eiver  Suspension 
Bridge,  Sew  York  City.   Fig.   64  gives  a  skeleton  idea  of   its  caisson  and  permanent 
crib.   Both  caisson  and   crib  are   of  timber  work.  The    caisson   is  divided  into  three 

• 

compartments  by  too  heavy  partitions  through  which  openings  have  been  provided 
for   communication  between  the  parts  of  the  working  chamber  .  The   caisson  proper 
is   20  ft.    in  depth,   the  permanent   crib   33  ft.,  and  in  this  53  ft.   the   foundation 
has  tertical  sides.  The  main  caisson  and  crib    timbers  are   12   in.   by  12  in.    The 
sheathing  consists  of  two   layers  of  3  inch  plank.   Diagonal  3  in.   by  12  in.    sticks 
for  so;ne  distance  above  the  wo  iking  chamber  give  beam  strength  to    tbs   caisson  roof, 
The   cutting  edge  is  shod  with  a  6  in.  by  8   in.  by  7/16  in.  angle  and  •£  .e    vertical 
edges  of  the  c  ai  sc.v:  end  crib  are  protected  v/ith  1  1/4  in.   bant  plates,, 

£::.V-IITE  AYE.    &V/IPG  BRIEGS,   N3"  YCH'"  CITY 

Fig.  65  shovs    u"  e   foundation   of  the  pivot  pier  o  f  the  Seventh  Avenue 
Bridge  across  the  Earlem  River   in  Hew  York  City.    The  caisson  is  cylindrical  on 
the   outside  and  octagonal   on   the    inside.    It   is  snnulax   ere.  has  a  clear  herd  room 
within  of  8  ft.   The   cutting  edge  and  outside  plates  are    of  steel  for  a  height  of 
15     IS,    The    side  plates   are  reinforced  by  1'2  in.    channel   struts  e.ixl    12.   horizontal 
I-beams.  The    inner   side   of  the    caisson  is    of  12  in.   by  12   in.   yellow  pine  sticks 

0 

running  vertically  sheathed  with  3  in.   plank.   The  caisccsi  roof   is    of  12  in.    by 
12    in.    sticks  sheathed  with  3   in.   plank.  A  trussing   7  ft.    deep  of  12    in.  by  12  in. 
pieces    supports  the   roof.  The  removable  coffer  dam,  a  polygonal  frame   of  sixteen 
sides  exists  above  the  elevation   -  11  ft,,    from  which  level   the  rock  fcced  part 
of  the   -3ier    starts.    Its  framing  is  clearly  inc'icrted  in  the  plan.   In  the   heert  of 


the   pier  is   found  a  cylindrical  mass   of  concrete   of  10    ft.    6   in.    radius  less  rich 
than  the  rest, it  consists   of  one  natural    cement,  2    sand  end.  5  broken   stone  to 
pass  a  2  inch   ring.   The  caisson   concrete   consists  of  1  Portland  cement,  2   sand, 
and  4  stone,  to  pass  a  1/2  inch  r  ing.  After  the    foundation  reached  rock   tot  ton 
and    the   caisson  was  properly  sealed  with  concrete,    the   interior  octagonal  mass 
of   soft    '-aterial  was  removed.    It  was   intended  then  to  pump  out    the  water    from   the 
central  veil   but  due  to  fissure?    in  the   rock  this  was  found    to  be   impossible  until 
these  passage  v;ays  for  water  from  without  were  thoroughly  filled  with  concrete  and 
grout.   The  lower  8  ft.   of  the  well  and  also  the   outer  portions    of  the   rest   of  the 
pier  were  .;nde    of  concrete  of  1  Portland  cement,    2  sand  ard  4   stone  to  pass  a 
1   inch  ring. 

An  article   on   the  Design  of  A  Railway- Bridge  Pier  by  C.Derleth,Jr.  , 
published  as  a  reprint    of  the  Engineering  I^ews  Publishing  Co.    1907,   is   to   be  con- 
sidered an  appendix  to  this  chapter.   Therein  are   given  the   principles   of  design 
for  a  masonry  pier   with  wood  coffer  dam  supported  on  crib  work,    tho    crib  work  in 
turn  resting  upon  a  rectangular  caisson  designed    in  structural  steel. 

ADDI TI OKAL  RKL7REFCES 

A.  BUILDINGS. 

1.  Foundations   for  'ftew  York  Municipal  Building;   by  Li.Deutsch,   School  of 
Ilines   Quarterly.,   Nov.  1910,   Vol.32;   Eng.   Mews , Vol. 63 ,   p. 24;   Vol.64,   p,    F-24 

2.  Pneumatic  Foundations    for  the  Gillender  Building,  New  York  City;  Eng 
News,   Vol.37,   p.    13. 

3.  Manhattan  Life  Building,  New  York;   Eng.    Record,   Jan.  20,  lb  94.,   p.li2. 

4.  Hydraulic  Caisson  Foundations,   Johnston  Bldg.  ,  Kew  York;   ^rgoRuoerd., 
Vol.32,   p.    117. 

5.    F.W. Skinner,   The   Development   of  Building  Foundations;    Eng.    Scccrd, 
Vol. 57, p.   412 

6,  T.K,  Thompson ,  Underpinning  the  Cambridge  Building;  Trans.  Am.  S^c. 
CoE.  ,  Vol.67,  p. 553.  The  Kew  Singer  Building  Foundations,  Trans,  Am.  3oc .  C.E, 
Vol.63,  p.  1, 

7..  Pneurartic   Foundations    of  the   Emigrant   Bank  Bldg.,    Eng,    Re<;jrdvVol .  60 
p . 528 . 

8.  The   Substructure   of  the  Bankers  Trust   Co.   Bldg,,  Eng.    Record., Vol. 62 
p. 677, 

9.  See  also  En;:.    Record,    Vol.65,   p. 105;  Vol.    66,  p. 320, 

10.    Recent  Developments    in  Pneuaratic  Found  rt  ions   for  Buildings,   by  DA., 
Usina,   Trans.   A.n.    Soc.    C,E,  ,   Vol.    61,   p.    211, 

B,  BRIDGES 

11.    Brooklyn  Caisson,  iJev;  York  arc.  Brooklyn  Bridge;   Ehg.    New?,,   irol     8, 
pp,.    182,    213,    224,    232, 


208. 

12.  Memphis  Bridge,  Mississippi  River,   Eng.  Sews,   Vol.27,  p.  470; 
Vol.   30,   p  509;   Report  by  G.    S.   Morrison, 

13.  C/U.n.^r  Bridge  Foundations;   Eng.  News,  Vol.28,  p.  222,  246, 

14.  Ti-e  Construction  of  the  South  Main  Pier   of  the  Quebec  Bridge,   Eng, 
Nev/s,   Vol. 65,  p.    3;>4. 

15.  Forth  Bridge  Report  by  ?.    Phillips. 

16.  Report    on  the  Washington  Bridge,    by  W.   R.    Button. 

17.  Report  on  the   St.    Louis  or  Eades  Bridge- 
C.    GENERAL 

18.  A  Concrete  Pneumatic   Shaft  at  Tower,  Minnesota     Eng.Record,Vol.62, 
p. 556- 

19.  Construction  of  Base  of  Baltimore  Light    in  Chesepeake  Bay,  Eng. 
Record,  Vol. 57,  p. 284. 

20.  A  Deep  Well  Sunk  "by  Caisson;  Eng.   Record,  Vol.61,  p. 696. 

21.  Dam  Foundation  Placed  by  Suspended  Pneumatic  Caissons;   Eng.  News- 
Kecord,   Vol.SS,    1013  ,p,  108. 

22.  Revised  Rules   on  Co/nprecsad  Air  Work   in  New  York;  Conference   of 
Engineers,  Contractors,   Workmen  and  State  Departments  adopts  measures   for    safety 
of  men  and  work;   Eng.    News-Record,  Vol.85,   1920,   p. 1225. 

23.  Experiences   in  Pneunjati c  Caisson  Sinking  in  Mexico,   Bridge  Pier 
Sunk  80  ft.   with  Green  Labor;   CaiP:;on  Provided  with  Open  Well    for  Dredging 
Simultaneous  with  Pneumatic  Work;   Sng«   Hews -Record,  Vol.87,    1921,   p. 848, 

24.  Stresses  in  Caissons  by  C,E, Fowler;  Ergineering-Contracting,   Vol.86, 
1921,   p.  1552. 

25.  Foundation  Problems  in  Srecting  Standard  Oil  Bldg. ,   30  Stories  High, 
Hew  York  City,  by  Ralph  H.    Chambers;   adjoining  nearby  buildings  underpinned  down 
through  cuicksand,   novel  method  of  coffer  darn  construction;  Eng.   News-Record, 
Vol.87,    1921,   p. 732. 


209 

CHAPTER  12 
DEEP  \VELL  DREDGING 

Constructing    foundations   by  the  deep  well  dredging  method  is  one  of  the 
oldest  known.    It   finds  wide  application,  and.  it  yields  excellent  results,    in  the 
greatest  depths  yet    reached.  The   foundation  structure  may  be  framed  of  timber  or 
iron,    or  steel,  with  the  closed  cells  in  either  case  filled  with  concrete,    or    if 
the    framing  is    of  timber,    they   are    sometimes   filled  with  gravel.    In  most  East 
Indian  practice  the  superstructure  has  been  built    of  masonry   (brick  or  concrete) 
usually  fitted  however  with  an   iron  cutting  edge.    The   open  cells  of  the    foundation 
structure   are  used  as  diredgi-ng  wells   and  they   remain  open  until  the  foundation 
bed   is  reached,      Reinforced  concrete  types  are  now  also  coming  into  use. 
POUGHKE2PSIE  BRIDGE,   Kgr.'  YORK;   TIMBER  CRIB  WELL 
EAST  OMAHA.     BRIDGE,   MISSOURI    ?IVER;  jgTAL_CAISSQH 

Figures   61   and  62  present    two  caissons   designed  for  the   open   dredging 
process;   the    first  shov.s   a  timber    framed   caisson  used  under   one  of  the  piers  of 
the  Poughkeepsie  Bridge,   Hew  York;    the   second  a  steel  open  caisson  under   the 
central  pier    of  the  East  Omaha  Bridge  across  the  Missouri   River.   As   shov;n  on   the 
plans  the  closed  cells   of  the    timber    caisson  were   filled  with  gravel.  As  the    steel 
shells  will  corrode  and  disappear  after  a  sufficient  period  of  time,  gravel    fillin,; 
should  not  be  used  for  a    steel  caisson,  but  concrete  must   be  employe-d  as  was  done 
at   the  East  Omaha  Bridge.   The  gravel   and  concrete  fillings  must  be  deposited  in   the 
closed  cells  during  the  process   of  sinking,   the  weight  being  required  in   that 
part  of  the  process,. 

An  examination   of   the  plans    shows  that  the   bottom  of  each  caisson  is 
shaped  or   framed  to   cutting   edges   formed   to   leave  dredging  chambers  with  sloping 
sides  leading  to  open  or   dredging  cells  or  wells  above.    These  cutting  edges  do 
not    offer  sufficient  bearing  surfe.ce  to  give  material    support  to  the  caisson. 
Herce  as  the    dredges   take  out  material    from  the    dredging  chamber,    the    imposed  dead 
weight   of  f-e  caisson  overcomes  the    friction  of  the -surrounding    -aterial   against 


210 

its  (Sides.  As  the  caisson  sirJcs,    the   inclined    sides  of   the    dredging  chamber    force 
the  .material  towards   the  center  of  the  chamber   and  this  enables  the  dredge  to 
readily  reach  it.    In  the  case   of  the    timber  caisson   the  wedge-like  walls  of  the 
chamber  are  usually,   though  not   necessarily,    framed  of   solid  courses  of  12  in.   by 
12  in.   timber.   Each    course   of  timber  is    laid  at  right  argies  to  those  adjacent    to 
it  and  they  are  all   thoroughly  drift  bolted  and   spiked  into  a  solid  mass.    These 
wedge  like  walls  might   be    framed   sufficiently    strong  by  leaving  interior  spaces 
to   be   filled  \vith  concrete.   It  is  only  necessary   to  design   them  in  view  of  the 
fact  that   they  are   the  portions  of  the  caisson  vhich  are  most    liable  to  damage  by 
coming  in  contact  with  boulders,    sunken  timber   ot  other  obstacles  whi c h  may  und er 
certain  conditions  produce  great  pressure  against     them.        It  is  therefore  necess- 
ary that  they    should  be  built  of  great  resi  sting  power.    The  walls  of  the    closed 
cells,    containing  in  this    case  3  ravel,  were   framed  in  this   particular   instance 
of  two   tiers  of   12  in.    by  12   in.    sticks  strongly  drift  bolted  and    spiked  together. 
During   the  progress   of  the  work,   these    ti  Tiber  walls  must  be  carried  up  sufficient- 
ly high  to    be  above  water  and  the  gravel    filling  must   be  put  uniformly  in  all  the 
pockets  so  that  uniform  sinking  may  be   aided.    If  the  weight   of  the  Structure 
itself  is  not  sufficient  to   overcome  the    side  friction  or  the  resistance  offered 
under  the  cutting    edges  temporary  loading-;  of  pig  iron  or  other  heavy  material  may 
be  employed.    Inasmuch  as  the   entire  foundation  structure    is    continuously  submerged 
while   sinking,  caulking  the   joints   between  the    timbers   is  not  required. 

The  construction  of  the   caisson  is  begun  at  the  cutting  edges;   the   upper 
walls  of  the   dredging  chambers  and  wells    being  built   up   first.   This  part  of  the 
v.ork   is  frequently   done  on  shore.   After  a  sufficient  poition  of  the    structure   is 
framed,    it   is     launched  and  the  remainder    of  the    framing  is   done  afloat.   The 
portion  of  the   structure    thus  completed   is   then  towed  to   the    site,    carefully  held 
in  accurate  position  by  Chinese  or   other  anchors,    piles,  frs.vied  platform  or  other 
suitable  means,  and   it    is    so  secured  until  it  has  penetrated  the  bottom  Ter   enough 
to  be  safely  held  by  the    surrounding  material. 

The  -orocesses   of  constructing  and   sinking  the    steel  caisson   (circular  in 


211 

plan,      fig, 62)   are   only  so    far  different   frcm  those  outlined   for   the  timber   caisson 
as  the   cteracter  of  the  material  requires.  The  steel  cylindrical  snd  c  onical    shells 
which  sta.Tt  from  or  unite  in  the  cutting  edge  are   first  carefully  riveted  together 
on  shore   to  a  convenient     height  arc",  then  launched.   I'M  s  portion  of  the  caisson 
may  preferably  be  made  v.i  oh  caulked  joints   around  the  dredging  chamber,   so  t  hat 
there  will  be  no  troublesome  leakage  whan  first   set  afloat.    This  portion  of  the 
caisson  may  also  be   fitted  with  a  false    timber  bottom  if  recessary   so  as  to  secure 
great  buojtancy.   It  will  generally  however  be  better   to  do  without   tMs   feature 

if  practicable.  After    the  lower  portion  of  the  caisson  surrounding  the  dredging 

% 

chamber  is  floated,   it  is  towed  to  the    correct  location  and   held  there   by  precise- 
ly the  seme  means   described  in  connection  with  the  timber   caisson.    It  is   then 
sunk  by  filling  the  annular  space   between   "ttie    two  concentric  shells  with  c  oncrete 
which  should  be  deposited   in  uniform  layers  9   to  12  ins.   thick   and  thoroughly 
rammed.   The    two  concentric  s lie lls  are   then  built   up  with  the   bracing  between  so 
as  to  receive  more  concrete  until  a  sufficient  portion  of  the  structure  has  been 
completed  to    enable    it  to  reach  the   bottom.   The    sides  are   always  carried  high 
enough  to  be  above  water   and  care   should  always  be   taken  to  keep  the  water  out 
of  the  annular  space  so  that  the  concrete  may  be  laid  in  the    dry.  After   the 

• 

cutting  edge  has  reached  the   bottom  the  operation  of  dredging  is  begun.   The  in- 
clined sides   of  the  dredging  chamber  will  force  the  material  toward  the   center   of 
the  dredging  well  as  the   caisson   sinks,   thus  enabling  the    dredge  to  reach  it.    If 
necessery  this  caisson  mcy  also  be    temporarily  loaded  in  order  to    overcome  the 
skin  friction  which   in  the   materiels  usually  penetrated  is  now  faiily  well  known, 
and   it  is  not  difficult   in  most   cases   so  to  (design  caissons  to  ualce   their   own 
.  weight  sufficient  to  produce   the   desired,    sinking  as   13- e    dredging  progresses. 

By  this   process  a  rock   bottom  cannot    in  general  be  r  eached.   A  rock  surface 
could  not.  be    satisfactorily  cleaned  if   a  level  portion   of  the  rock  should  happen 
to  exist,   although  divers  might  be  employed  in  depths  of  Vvater  not  too  great  for 
their  working.  As  a  matter  of   fact  little   or  no  level   rock  surfe.ce  exists  under 


212 
foundation  structures.   It  isnot  practicable  to  level   or  finish  in  steps  the  :  .c  . 

bedrock  that  might  exist  below  the  dredging  chambers  of  the  caisson.  It  is  there- 
fore usual  to  sink  the  caisson  into  sane  solid  stratum  of  material,  suchas   sand, 
gravel   or  hard  clay  or  a  mixture  of  those  materials   or   of  others  having  sufficient 
resisting  or  bearing   capacity  to  carry  the   imposed  loading.  At  most    sites  where 
thi^process  can  be  applied  it   is   seldom  difficult   to   find  such  strata.    Foundation 
beds  of  this   character   ordinarily  lie  underneath   softer  materials  suchas  mud 
or  silt  and    it   is   imperative   that    the    cutting  edges  of  the  caisson  penetrate  so 
deeply  into  the  bearing  stratum  that  they  can  in  no  way  be  reached  by  the   scouring 
action  of  a  v,ater  current.    It  is   very  e  ssential    that   this   feature  of  any  location 
selected  be  most  carefully  and  thoroughly  considered  for  among  other  things,  the 
presence   of  piers  will  cause  increased  contraction  of  river  section  and  will  tend 
to  produce  increased  scour.   In  case  the  river  bottom  is   of  send  or  silt  it  may 
be  subject  to  comparatively  large  soil  movements  to  considerable  depths  in  the 
riyer  bed;  as  is   constantly   the  case   in   sediment  bearing  rivers  subject   to   floods. 
In  the  application  of  open  dredging  to  most  conditions   it   is   imperative  to    fafetyl 
that  the  caisson  be   sunk  a   considerable  distance  below  the   lowest   scour. 

There   are  instances  where   the  bearing  stratum  is  of  sand  with  mud  and 
silt  above  it   in  which  the  penetration    into    the    sand   has  not  been  more   than  8  to 
10   ft.   The   stability   secured  by  such  a  shallow  depth  of  penetration  is  more   or 
less  uncertain.  Other  cases  exist    in  vhich  the  penetration  into  the    sard  is  a  s 
ranch  as  40  to    50  ft.   In  these    latter  instances  there  was  very  little  .nud   or   silt 
orer   the    sand . 

After  a  suitable   depth  has   been  reached  in  the    stratum  which  is   consider- 
ed to  yield  a   satisfactory  foundation  bed,    the   dredging  chamber  and  dredging  wells 
are  filled  with  concrete.    Inasmuch  as  the    foundation  bed  will  not  be  o  f  rock,  a 
very  close  boni  between  that  bed  and  the  concrete  will  not  be   secured.   It   is 
however  essential  that  as  much   soft  material  as  possible  shall  be  removed  from  th-- 
dredging  chamber  so  that  the  first   layer  of  concrete  deposited  under  water  shall 
suffer  as   little   deterioration  at  its  under    surface  as  possible .- The  deposition 


213 

of   this   concrete    through  the  water  of  the  dredging  chamber  must  be  conducted wi 
all    ohe  care  vhich  has  already   been  prescribed  for   that  work.  It  may  be  necessary 
at  some   points  to  deposit  a  portion  of  the   concrete  in  bags,   but  in   general  it  will 
only  be  necessary  to   deposit    from  as   large  buckets  as   the  dimensions  of  the  work 
will  permit,  until  all  the   dredging  chambers  and   dredgingwwlls  are    filled.    If  the 
caisson  is    framed  of  timber,    it  will  be  necessary  to  place  a   coffer  dam  at   the  top 
of  it  in  which  the  neat  ,.:asonry  of  the  pier  will  be  started.   This  is  a  requisite 
feature  of  construction  for  the   reason  that  it  is  necessary  to  keep  all  pernarent 
timber  below  the   lowest   low  vater.    The   coffer  dam  will  be  framed  on   the    top  of 
the  permanent   timber  work  of  the  caisson.    Its  sides  will  be  of  the  same  general 
character  aid  may  be  held   in  place  in  the  seme  general  way  as  the    sides  of  the 
open  caissons  described  in  Chapter   10;   or   the    detachable  coffer    dams  referred  to  in 
Chapter  9. 

If   the  caisson  is    framed  of  steel,   fig. 62,    it  may  either   be  carried  up 
to    high  water   or   stopped  at  low  water,    or  carried  up  continuously  to  the    top  of 
the  finished  pier.    In   the    latter   ccse,    the   masonry  of  the  pier  up   to    the   coping 
course  will  be  of  concrete  r.nd   it  will  be  advisable   to  have  the   surface   finished 
with  cut   stone  at  tih.e   points  where  the  bridge  superstructure  may  rest.    The  dredging 
wells  and  dredging  chambers  are   filled  with  concrete  deposited  under  water  pre- 
cisely as  already  described  for  the   timber  caissons.    If  the    steel   caisson  be  used, 
it  should  be  borne  in  mind  that    the    iron  or  steel  portion  will   eventually  corrode 
anl  disappear,  although  many  years  may   elapse  before  that   operation  is   even 
partially  completed-    It  is   essential  therefore  in  designing  the  steelwork  of  the 
caisson  that    the  continuity  of  the  concrete  masses  which   form  so  large  a  portion 
of  the  vhlurae  be  as  little   trenched  upon  as  possible.   It  is  not  of  serious  moment 
whether  the  plates  and  gngles  or  rods   eventually   corrode  away  if  enduring  masses 
of  continuous  concrete   so  remain  in  place  that  they  do  not  change   their  positions 
in  reference  to  e  ech  other.   Vertical  partitions  running  entirely  or  any  materiel 
distcnce  across  the  pier  should  be  avoided  as  their   disappearance  by  corrosion 


-•'?:.. ..".-c     .-    ...  ,. 
^    '*..- 


'-ii  »J--T;lf??*-i££J't6j    ':  o"T?T'.';''        •  - 
r^  -_..^.-^:i;ii  i .':  ^    '.^oS'i      V:   ^^       -•  '-c  •  • 

-  - 
'"'  '  "  ..     •        i 

-,    /:   ,.;.,,          •.    y     ..--,. 'i.-o^    JJ^I    VC^:J   ^'  f'Vls 

-'•  •-  -  •  --" ;    ;-~  • 


.  •.    .-:.    .  >         :.ji,_^-. 


214 
would  tend  to  separate  the  masses   of  concrete.   As  the  plans  show  in  the  present 

instance  the   only  interior  partition   of  steel  is  the   shell  of  the  dredging  well 
which   is  concentric  with  tfee   outer  shell.    The   corrosion  of  the  former    therefore 
would  leave  tho  concrete   of  the  centralwell  a   continuous  mass.  Only   the  bracing 
angles  and  rods  are    found  between  the  two  c  oncentric   shells  end  they  may  entirely 
corrode  away  still   leaving  concrete  in  the  annular  space  practically  continuous. 
These  considerations     should  govern  all  designs  of  stoel  caissons  whether    fbr  the 

open  dredging  process   or   for  any  other  method. 

of 
It  would  conduct  to   the  durability  of  all  timber     caissons  or, other 

timber  structures  under  water  to  use  wooden  tree  nails  or  pins  of  suitable  size 
for  timber  framing,  instead  of  iron  or  steel  drift  bolts  or  spikes  aid  they  are 
sometimes  used  for  sub-aqueous  timber  work.  In  most  instances  however  this  pro- 

t 

cedure  seems  unnecessary,  at  an^/  rate  it  is  not   often  followed. 

In  designing  open  caissons   it   is    essential  to  the   best   dredging  results 
that   the   number  and  location  of  the  dredging  wells  be  most  carefully    considered. 
In  order  that  the    caisson  shall    sink  vertically  it    is    imperative  that   It  bo  . 
pOBdiblo  to  dredge  at    different   points  v.lthin   the  oxtorior  limits  of  the  cutting 
edge.    If  tho   material   is    harder  under   one  portion  of • the  caisson     than  under 
another,   it  may  be  necessary   to  dredge   tho  hard  portion  ahead  of  the    softer.   Again 
if  one  side   of  tho  Crisson  settles    faster  than  the   other,    it  will  bo  necessary  to 
dredge  on  the   latter   side  ahead  of  the    former  until  the   error  ±a  motion  is  correct- 
ed.     Similarly  other  conditions  mr.y  arise  under  which  it   is   advisable  and   fre- 
quently absolutely  necessary  to   correct  an   error  of  moti  on  by  dredging   in  one 
particular  portion  of  tho  cutting  odgo   area  rather  than  another.    Tho    caisson 
therefore  should  be   so  arrargod  that  this   choice   of  the  dredging  points  may  bo 
exercised  as  widely  as  possible.   At  the    same   time   tho  number  of  dredging  wells 
should   bo   reduced  as   far  as  the  preceding  considerations   will  permit.   It  is  ovideu" 
that  the   disposition  of  the  dredging  wells  will  bo  affected  by  the    shape  of  tho 
caisson.    In  case    of  the    circular  caisson   of  Fig. 62   one    largo  circular  well   is  the 
be'st  arrange. rent,  whcrors  in  Fig. 61,  a    considerable  number  of  wolls  were  wisely 


215 

used.   The   inclination  of  -the   sides   of  the   dredging  chamber   should  not.be  too 

great   to    the  vertical   in  order  that  the  niaterial  in  the  chamber  may  offer  as  little 
resistance  to  sinking  as  possible  and  that   at  the  sane  time  the  material  may 
readily  be  forced  into  reach  of  Hie   dredging  bucket.  No  definite  \alue  can  be  given 
to  that  angle  but  it  probably  should  seldom   exceed  30  to   35  degrees.   The  pottion 
of  tl-.e  plan  of  the  caisson  taken   for   the   dredging  wells  will  bo  affected  by  the 
amount   of  weight  to  be   secured  to    overcome   the  fractional   resistance  of  the  sur- 
rounding material.   If  the  dredging  veils   take  up  most    of  the  volume  there  will  be 
but  little  weight  available    for   sinking.   On  the    other  hand,    if  they  arc  too  small 
the   operations   of   the  dredge  will  bo  prejudiced.  A  careful  br.lr.nco  between  these 
services  must  be  secured  in  view  of  the    features   of  each   case. 

It  has  sometimes  been  thought  advisable  to   batter  materially  the   exterior 
surfaces   of  these    caissons.  A   little  batterirg  may  be  given  to    the  upper  portion 
if  desired,   but  at  least  the   lower  portions    for    a  considerable  distance  above 
the  cutting  ed~e  should  be  cylindrical,   that  is,    opposite  sides  should  be  parrllel 
and  vertical.    If  the  batter   of  the    sides  coranencos  at  or  near   the    cutting  edge 
the    caisson  will  be  held   truly  vertical  in  sinking  only  with  great  difficulty   if 
at  all.   Host  serious  trouble   has  arisen  in  some  cases   in  conseruenco   of  such  a 
feature  of  design,    There   is  probably  very  little    decrease   of  resistance   if  any 
secured  by  battering  even  the  upper  portion  of  the   caisaon*  Liuch  more  steadiness 
and  accuracy  of   sinking  will  be  secured  by  making  the    cai  ss  m  cylindrical  in  its 
general    form,   anc?    if  any  portion  of  the   exterior   surface  is   battered  that  portion 
should   begin  at  a   considerable    distance  above   the    cutting   edges,   as    shown  in 

Fig. 61. 

The   depths   of  penetration  reached  by  this   process  up  to    the  present  time 

have  a  ;vsxi:-aum  (for  bridge  piers)   of  about   170   ft.  to  nearly  200  ft.    below   the 
surface   of  'the  water.   The   abnormal  pressure  on   the   foundation  beds  when   the  latter 
are   sand  have   in  some   instances   been  as  high  as  11,400  Ib .  per   sq.    ft.    although 
it   is  more  corcmon  to    fine",   the   abnormal  lords   imposed  on  the    foundation  beds  run- 
ning from  about  5000  Ib.    to   8000  Ib.   per   sq.    ft.  without  any  deduction  for    skin 


216 

friction,  but  with  deduction  for    buoyancy  for   the    foundation  material  in  water. 

Theoretically  the  open-well  caisson  can  be  sunk  to  any  depth  provided 
suitable  granular  :r,aterial    is  encountered.    Practically  tl?.e    depth  is    limited  by 
the  weight   required  to   overcome    the    skin  friction  on  the  sides   of  the   caisson  and 
by  obstructions  offered  to   the  cutting  edge.   The  greatest  depth  -recorded  for  an 
open-well  caisson  is    for  a  mine  shaft  in  Germany,  which  was  sunk  256  feet. 

In   the  Omaha  foundation,   Fig.  62,  a  system  of  3  in.   jet  pipes  20   in 
number  opened  into  the   dredging  chamber  ner,r  the  cutting  edge,  being  reduced  to 
1  inch  at  that  point.   Those  pipes,    imbedded  in  the  concrete,   were   cesried  vertical- 
ly £o  the  top  of  the  cylinder.  At   intervals  of  10  ft.   vertically  a  connection  was 
made  fro  :U  eech  pipe  -through  the   outside   shell   to   the  exterior  of  the  cylinder  by 
means  of  a  3/4    inch  pipe.   This   system  of  water  jets  helped  to    reduce   tho  friction- 
al  rosiste.rce    both  for   ths   sides  and  cutting  edgo  and  eidod  in  controlling  the 
descent   of  the  caisson.    See  Eng.   Record,   Vol.30.,  jferch  3,1894,  p.   218, 

HAYJKESBUBY  BRIDGE,   MEW  SOUTH  TOi 


The   Hawkesfeury  Bridge  in  Australia,   Fig.62A,  had   its  piers   sunk  by  tho 
deep  well  dredging  process.    These  piers  are  rernrrkable    for   the    depth  of  foundation. 
The   metal  shells  are  20  ft.  wide  and.  48   ft.    long   in  plan  between   semicircular 
ends.   Each  pier  was  provided  with   three  dredging  w  el  Is,    each  well  8   ft.    in  di?m= 
The  deepest  pier  rests   on  a  bed  of  Ir.rcL  gravel  126   ft.    belov;  the   river  bottom, 
185  ft.    below  high  vat  or  and  227  ft.    below  tho  track   of   the  bridge.   See  Eng.  News 
Vol.    15,    1886,  pp.  98-100;    also    Baker's  Masonry  Construction,  p.  425;  rnd  Fowler's 
Ordinary  Foundations,  pp.  94-96. 

COHCHETE  CAIBSOF-SPILLVt.Y,  C..L..VER.S  ILM 
SPRIHG  VALLEY  U..TER  COIJRiJSY 

On  March  24,1918,   the  Calaveras  darth  dam   fe.il  ed.    Cf.    Eng.  Sews-Record-, 
Vol.80,  pp.631,    679,   692.,    704;   Vol.81,   p.  1158;  Vol.82,   p.  487,    It  was  being  cai- 
structod  chiefly  by  the   sluicing  method  with  some   dry  material    dumped  from  cars 
in  the    dovmstream  fc.ce. 


217 
Nearly  the  entire  upstream    slope  of  the   partly  finished  dam  was 

completely  displaced  by  being  pushed  outward  and  downward  fir  an  its  normal  position 
into    the   reservoir    to  a  maximum  distance   of  about  400    ft, 

The  top  of  the  completed'.  dsm ,    25  ft.    in  width  >  was  to  have  elevation  810, 
or  approximately  235  ft.  above  the   bed   of  fee  creek,  elevation  575.   The  upstream 
slope   VB.S  t  o  be   1  vertical  to  3  horizontal  and  the    downstream   slope  was   1  vertical 
to  2   1/2  horizontal.   The  concrete    storm  water  conduit  of  horseshoe  shape,   19'6" 
x  19*6",  was  built  approximately  along  the   line  of  the   creek  bed   from  the  toe  of 
the  dovzistream  slope  to  the   toe  of  the  upstream   slope,   fitted  \1  th  temporary  gates 
at  the  upper  end  aid  connected  with  a  concrete  outlet  tower   about  250  ft.   high,      , 
that  is,   with    the    top  of  the   tov«r   above  high  water  in   the    finished  reservoir. 
Fig. 69  shovs  roughTy   the   connection  between  the   tower    and  the  end  of  the  horseshoe 
conduit. 

The   tower  was  situated  on   1he  upstream  toe   of   the  dam.   It  rested  on  rock 
at  elevation  576;    its  reinforced   concrete  base  vwas  an  octagon  of  50  ft.,  diameter, 
The   base  slab  was  9  ft,    thick.   The  cylindric  tower    shell  began  therefore   at 
elevation  585,  with  4   ft.    thickness  of  shell  and  28   ft.   outside  diameter.    The 
shell  tapered   to   a  thickness  of  12"' at   the   top  at   elevation  805  with  an  outside 
diemeter  of  12  ft.    Both  the    base   and    shell  were  very  heavily  reinforced,    like  a 
reinforced  concrete  chimney.    The  tov.'er  was   designed  to  withstand  in  addition  to 
other   stresses,   the  effect  of  an    earthquake  acceleration  of  6  ft.   per   sec.    per  sec. 

The  sliding   earth  at  the    time   of  the   dam   failure  produced  so  great  a 
pressure    that  this   concrete  outlet  tower  was  overthrown,    the    shell  being  ripped 
from  its  base.    It   vsas  moved  far  out   into   the    lake. 

At  the    time   of  the  slipping  the  water  in  the  reservoir  stood  at  elevation 
652.   Fortunately   the   entrance  to    the  horseshoe  tunnel  was  clogged  with  debris 
after  the  tower   failed,    so  that   v.ater  ceased   to  escape. 

It  became    immediately  necessary  to  protect  the   injured  dam  from  future 
flood  voters.    Two  precautionary  measures  were   at  once  planned:-  1.   a  horseshoe 
tunnel  8  ft.   in  diamo.ter  was   driven   through   the    solid  hillside   to    the  west   of  the 


218 

so  that   the    reservoir  might  be   drained  to  tho  stream   below  the  dam;  2.    it  was 
decided  to    sink  a  shaft  through   the  mass   of  material  v.'hich  had  slipped   from  the  dam 
find--*!hich  over lr. id  the    site  of  the   overthrown  outlet  tower, 

Fig.   69  exhibits  this  shaft  which  was   essentially  sunk  by  the  dredging 
process  though  little  wr.ter  was  encountered   since  the    structure  was   sunk  after   the 
•reservoir  lir.d  been  drr.indd  by  the   8   ft.    tunnel  already  mentioned. 

The   slipped  material,    after  the    dam  failure,   had  a   surface   elevation  of 
about  655  £t  the   outlet  tower   site.    Therefore  it  vr.s  necessary   to  penetrate  ver- 
tically through  rbout  70  ft.    of  nr.terial   to  elewtion  585  at   the    base   of  the.fr  Hen 
tower.    It  vr.s    doterminod   to    biild  this  sir. ft  as  a    temporary  structure  rnd  only   to 

olcvrtion  665' since   for   the  present    water   could  not  safely  bo  impounded  to  greater 

i 
heights  in   tho  reservoir   because   of  tho  wrecked  condition  of   the  dam. 

It  vas   first  necessary  to  excavate   the  ground  to  give  a   level    space  upon 
which  to  build  up  the  cutting   edge  for   the  caisson  spillway   shaft.  The  cutting 
edge  consisted   of  si;scl  plates  sot  by  bolts  with  pipe   s  leaves ,    shown  in  Fig.  69, 
by  "plan   of  shoe"  anO.  "section  of  driving  shoe".   The    spree  between  the  plates  was 
filled  v.lth  concrete.    Jlio  caisson  shaft   is    a  right  cj .Under   16  ft.    outside  diam, , 
concrete  shell  2  ft.    thick;  with   sufficient    reinforcement   both  vertically   and 
horizontally  to  give  'iho  structure  toughness,    not   so  much  against    lateral  pressures 
of   earth  or  water ,   but    to  ir.r;urc  sufficient  strength,  to  the   cylinder    against 
sinking  strains.    The   sin, ft  ras  built  in   sections  using  a  set   cf  stool  forms  5  ft. 
deep.. Those    forms  were  us?d   over  and    over  again  until   tho   entire    shaft  ws  ccm- 

.     pleted. 

Workmen  excavated  mate-rial    frcm   inside  the  shaft,  which  vr.s  token   out  by 

bucket  and  derrick  hoist.     J.s  tho  oxcavr.tion  proceeded  the   shaft    sr:nk  under   its 
own  weight.  Ls  it    sank,  additional  units   of  its  height  were  poured  tc  keep    tho  top 
always  above  the  ground   surface. 

Provision  was  made   by  pipes  in  tho  concrete    to   allow   of  water  lubrication 

i 

at    the    cutting  edge.  But  little  difficulty  vr.s  encountered  in  sinking  tb  c  shaft. 

7,'licn  the  cutting  odgo   reached  olsvr.tior  rjb:iut   585  sinking  vr.s  stopped  rnd 


219 

the    shaft  thoroughly  sealed  with  concrete    to    form     a  \vater   tight  joint  v/ith 
concrete  base    of  the    old  outlet   tower.  At  the    same   time  a   ccmpleto  connection 
was  made  by  excavation  and   tunneling  between  the   new  spillway   shaft  and   the   old 
horseshoe  tunnel.    The    details  are   sufficiently  shown  in  Fig.  69;   see  "Slevation 
and  section  through  adit". 


1.  J.Newman;  Notes    on  Cylinder  Bridge  Piers  and  the  Uell  System  of 
Foundations;  published  by  Spon  and  Chamberlain. 

2.  Foundations,  Abutments  and  Footings;  Hool  &  Einne;   article  on 
"Open  Caissons"  by  J.   C.    Sanderson,  pp.    114  -  122. 

3.   Open  V/ell  Piers  and   Subdivided  \7arren  Trusses   of  Bismarck,  Man  dm 
Bridge;  Eng.  Kov/s-Record,   Vol.    88,  p.    180  = 


220 

CHAPTER  13 
DEEP   FOUNDATION  PRESSURES 

The   determination  of  pressures  is   a  complex  problem  when  investigating 
horizontal  joints  at  increasing  d  epths  in  deep  foundation  structures,   such  as 
bridge  piers  aid  high  masonry  dams.    Distinction  :nust  be  nr.do  between  absolute 

• 

pressure  on  the    foundation  bed  and  abnormal  pressure   on   the   seme;   see  these  notes, 
page  47.   When  a  pier   is   submerged  in  water   or   granular  nr.terial  impregnated  with 
water,  v;e  must  consider  the   effect  of  buoyancy.   Water  may  introduce  itself  under 
pressure   at  any  joint  or  at  the    foundation   bed..    In  such  cases  the  moment   of 
stability  from  gravity  loads   is  •  considerably  decreased.  The   determination  of 
buoyancy  effects  however    is  quite   uncorta in  sinc-e  we  must   assume  tho    degree  to 
which  water  pressure  may  bo  oxcrtod  within  aid  under   the  masonry  mass  or  at  its 
foundation  bed.    Consult  Corthcll,  Allowable  Pressures  on  Deep  Foundations;  also 
those  notes,   pp.   47-49. 

In  Chapter  4  pp.    58-66,    the  stresses  on  a  horizontal  joint  have  been 
investigated  and   formulas  written   for    stability  against    (l)    sliding;    (2)    overturn- 
ing;   (3)  vortical  pressure  or  crushing.    It  can  be  shown  hov.evcr  by  the   general 
theory   of  stress  the -t  the  ;naximu:n  effects  do  not  necessarily  occur  on  a  horizontal 
joint.   There  -re?.y  bo  at  some  point  in   the  nasonry  mass  a   .greater  shear  or  pressure, 
or  even  a    tension,   on  a  plane  inclined  to  the  horizon.  Those    observations   apply 
particularly  to  structures  like   high  retaining  walls,    or  bettor,  high  masonry 
dams .  which  a  re  subject  not   only  to    gravity,   buoyant  and    other  vertical    forces, 
but  also  to  groat  horizontal  thrusts  from  water  or   crrth  or   ice.   Consult   tho 
following  references: 

1.  Morrison  and   Broclie;   Masonry  Darn  Design,   Chap.    8,   p.    169. 

2.  V7.   C.  Unwin,   on   the  distribution   of  shearing    stress  in  masonry 
dams;   Engineering,   Vol.    79,  pp.   414,   513,    593,   825. 

3.  Cta.   Cain,   Trans.   A;i.   Soc.    C.  E.  ,   Vol.   64,  p.    208. 

4.  L.  W.Atchorly  and  K.Pearson,  Or.  Some  Disregarded  Points  in  the 
Stability  of  .fesonry  DT.^JS;   Proceedings  Inst.   C.L.  ,  Vol.    1625   p. 456. 

5.  O.L-Brodie;   ifc.sor.ry  Dam  FormuL-s;   Columbia  University,   School  of 
Mines  Quarterly,  Vol.    29,  p.   241. 


.  - .-.-.- 


i     ,     . .     S-  i        f     -       •' .        ...  *•     . 
...    J    L        •       ,         . 


•••     :  "";"    "•'•"- 


221. 

6.  Stresses  in  Masonry  Dams;  Eng.   Record,  Vol.57,  p. 162. 

7.  Experimental  Investigations  of  the  Stresses  in  Masonry  Dems   Subjected 
to  Water  Pressure;  by  J.Y/.Ottley  r.nd  A.W. Brightmoro;   Proceedings  Inst.   C.E.  , 
Vol.   172,   p. 89. 

8.  Stresses  in  Dams;   An  Experimental  Investigation  by  Moans    of  India 
Rubber  Models;  by  J . S.W  i Is  on  and  W.Gove;  Proceedings  Inst.    C.E. ,  Vol.172,  p. 107. 
See   also  Engineering,  Vol.80,  p. 134. 

9.  Stresses  in  Masonry  Dams;  by  E. P. Hill;  Proceedings  Inst.  C.E.  ,   Vol.172 
p. 134. 

10.   Bligh;   Dams  and  Weirs;  Art.    22,  p. 27;    formulas   for  maximum  stress. 

In  the    following  analysis,    Fig. 68,  only  vertical    loads  are  considered. 
The   forces  W  can  be  treated    to    include  not  merely   dead,    live  aid  buoyant    forces 
but   also    the    effect    of  side  friction   as  in  the    case    of  piles  or  cylinders;   yet 
because  the  masonry  dam  or  pier  under  present    consideration  is  relatively  so 
massive  and   large,   it   is  on   the   side   of  safety   to  neglect  the   effect  of  side 
friction  by  assuming  that    eventually  the  mass  adjusts   itself  to    its  surroundings. 

The  analysis  given  does  not    involve  the  effect  of  lateral    forces,   such  as 
water  thrust  on    dams ;    earth  thr us t    agrinst  retaining  walls;    arch  or  dome   thrust 
for  abutments   or  buttresses;    ice  thrust  against  dras,    bridge  piers  or  water 
intake  towers;   current  pressure   upon  piers;    or  wind  pressure  on  towers'  and  chim- 
ne"S.   The   dynamic  effect  of  wave  action  against  dams  is    a  special  case  which 
might  also   bo  iicntioned.    Further,   in  retaining  wall  and  abutment  structures  with 

unequal   lateral  pressures  on  the    two    sides   (as  in  the  case    of  an  arch  bridge 

\ 
abutment  which  has  arch  thrust,  water  and  earth  pressure  on   one    side  and   only 

crrth  pressure   on  the   other)  there  might  be  considered  the  effect  of  abutting 
power  of   earth  on  tho    land  or  approc.ch  side   assisting   to  withstand  the  arch 
thrust.      But  in  conservative  practice  such  a    procedure  would  not  be  allowec"., 
though  its   effect  must  contribute  largely  to   the   lateral    stability  of  deep  abut- 
ments. 

In  Fig. 68  let  tho  pyramid  of  blocks  represent   a  deep   foundation,   for 
example,  a   bridge  pier.  AB  is    tho  lovol  of  the  pi  or   top;   h  its  height  above  tho 
mean  water  level  CD.    Let  EF  bo  the  water  bottom.    Let  the  material  b  etwocn  the    lovr.-. 
EF  and  GH  be  mud,  weighing  m  Ibs.'pcr  09. ft,     Assume  tho  water  weight    f  Ibs.  per 
cu.ft.   Lot  the  material   between  the    levels  GK  and  JK  be  sand,   of  s  Ibs.   per  cu.iv . 


»    ,  '  •  >';•',  -,v 

'. 


••• 


••••- 

i   -/,. 

JU    .>    j 

•    :  j"  • 


.    ,- 

!  '.'• "      '      ' 


222 

v/oight  and   aippose   JK  to    be   the  rock  surf  re  o   or    foundation  bo:1.    Lot  W  represent 
tine   total  weight  of  superstructure  resting  upon  the   pier   top  or    first   block;  ¥]_ 
the  total  weight  resting  upon   tlie    second  block  and   so  on.    Let  hi,   h£,  h3,   etc.    be 
the  heights  of  the    several  blocks   beginning  with    the  top.    Let  AI,  Ag,  A3,   etc,    be 
the   base  areas,   and   ti,   t2,   ts,    etc.    the  v.ldths   of   the  same  blocks  respectively, 
Let  p  be   the  allowable  intensity  of  pressure    at  the   br.se   of  the    first  block; 
let  w  be  the  weight   of   its  :rr.torial  per  cu.ft.,   and   c     a  coefficient   indicating 
the  relative    dimensions  of   the  plan;      cti   is   tie  block's  width  at   right    angles 
to  the  plane   of   the  diagram.  Therefore  AI  =  cti2,      Lot  p.   bo  the   allowablc- 
pressure  intonfeity  and  v/i  the  weight  per  cu.ft.    of  the  material  of  all  remaining 
blocks.   Let  c  have    tho  s  rmc  significance  for    those   blocks  as  for   the    first.   Here 
a   distinction  is  made  between  PI  and  wi  for  tho    foundation,   and  p  and  w  for  the 
cap   or  coping.   Usually  P>  Pi°     If  the  upper  part  of  a  pier  were  concrete  and   the 
lower  part  of  timber  crib    filled  with  concrete,    then  the  two  parts  would  have 
different  values   for  pi  andv/i;   the  crib   work  taking  lessor  TCluos  for   each. 

• 

Again,   tho   vc. luo   of  c  might  be   different    for  different  blocks.      Too  much  variation 
has  been  avoided  so   that  tho  equations  would  express  principles  without 
prolixity, 

Tho  load  upon  the    base   of  tho  first  block  then  is:- 

1/i/l  =  v7  +  cti2hiw  -  cti2   (iil-fr)f  •    •    •    -    •    • (l) 

Hero  cti2   (hi-h)f  is   the  weight    of  displaced  water;    it    rets   only  with  its    full 
amount  when  water  gets  freely  into   the   joint   at  the   base   of  the  block.   Ehoorotical- 
ly  this  quantity    should  be  affected  by  a   coefficient  k  depending  upon  the  degree 
of  porosity  of  the   joint;  k  would  then  vary  between   zero   and  unity.    For  high- 
values   of  k  the  pressure  v/ould   be   smaller  in  the  pier  but    the  lighter  effective 
weight  would  give   less  lateral    stability  against   overturning  agrinst  horizontal 
forces.  This    ;atter  of  buoyancy  is    of  most    importance  for  the  joint  at    the  rock 
sur  face . 

In  rccc-nt  analyses    for  high  masonry  dams   it   is    custo;ir  ry  to  assume   full 
buoyant  water  -oressurc   at   the  upstream  edge  of  the    joint,   with  an  intensity  of 


225 

pressure  decreasing  line-ally  to  zoro  at    the   downstream  edge.    In  any  case  tho 
distribution  and  cmount  of  such  prossure  from   Ic-akage  of  wrter  under  the    struc- 
ture must  depend  upon  assumption  and  that  assumption  must  bo  a  matter  of  judg- 
ment   in  erch  particular   design.   It  is    now  customary  in  great  masonry  structures 
like  darns  to  provide  interior  channels   or  galleries  into  v*uch  to  drain  off 
lerkage  with  the   idea  that    such  moans   rill   reduce  to   a  minimum  any  buoyant, 
action,   Consult: 

1.  J.  R.  Freeman  -  Some  Thoughts  Suggested  by  tho  Austin  Dam  Failure; 
Eng.  Hews,   Vol.66,  p. 462. 

2.  C.    L.Har:  ison  -  Provision  for  Uplift  and   Ice  Pressure   in  Designing 
Masonry  Dams  -  Trans.  Am.   Soc.    C.E. ,  Vol.75,  p. 142, 

3.  F, P. Stearns,-  ifcsonry  Dams   and  Their  Foundations;  Eng.   Record,  Vol.64 
p. 492. 

4.  E. Wogmann  -  Tho  Design  of  Masonry  Dams;   Should  Hydrostatic  Pressure 
Underneath  and   Ice  Pressure  be  Included?  Eng.  News,  Vol.66,  p. 594. 

In  recent  years  much  attention  has  been  given  to  the    study  of   therraal 
Stresses  in  masonry   structures.    There   is  no  doubt  that  some  crumbling,  rupture 
or   shearing  may  be  due  to   this  cruse    as  well  as    to  the  effect  of   ice  pressure 
from  freezing  w ate r  which  has   found    its  way  into  a  crack   or  fissure.   Consult: 
C  S.G-owen,    The  Effect  of  Temper  ature  Chr  nges  on  Masonry,   Trans.    Am.   Soc.   C,E,  , 
Vol. 61,   p. 399, 

The  greatest  allowable  pressure  upon  the  br.se  of  tho  first  block  is 
cti2p-,  and  this  quantity  must  be  equal  to  or  greater  than  eq.  (1).  ^SSU-TB  it 
ecusi  thereto,  then, 

~i          ~~~~  '    (2) 


,  i 
if 


PI   *  c(lii-h)f  - 

Equation  (2)  give?;  the   -v/alue  of  t^  and  thus  we  also  know  A^  and    the    total  weight 
Alhlw  of   the    first  block.    The   lord  upon    the   br.se  of  the  second  block  is:- 

W2  =  Wl   +  Ct22h2   (wx-f)  ^  ct22pl   ...........       .    .    .....    (3) 

ct£2pl  is  the   greatest    allowable  pressure  upon  the   joint  Ag« 

In  equation   (1)    it  is  assumed  that  water  gets   freely  into  the  joint  A^ 
thus  k  =  1  for    that  joint.    If  buoyant  action  is  only  partial  k  lies  between   one 
and  zero.    If  no  water  enters  joint  A1?  k  =  0.   In  general  :- 
Wl  =  \7  +  cti2hiw  -  kcti2  (hl-h)f, 


~       - 


I      -, 


.  ..'.-i    .' 


224 

In  good  masonry  water   cannot  enter  the  joints   freely  rnd  therefore   the 
tera  containing  I:  is  generally  omitted,    the    assumption  bein0  further  on  the 
side   of  scfety,  when  only  vertical   forces  v/  act.    If  there    are  horizontal  thrusts 
then  lighter  pressures  on  A  give   less  moment  of  stability  against  overturning. 
Similar  rencrks .    regarding  k  apply  to    lower  joints. 

From  equation    (S)  neglecting  the  inequality :- 

.-..-. (4) 


Af 

y 


-  ch2  (v/i  -  f  ) 
In  1  ike   nr.nner  : 


cPl  -  chg    (Y/!  -  f  ) 
where  rigorously  W2  =  Wl  +  ct22  hg^i  -  kct£2h2f  .   Similr.rly:- 


*4   =  W3  .................    (6) 

/I  - 

cp]_  -  ch4(v/i  -  f  ) 

It  is  r.ssvmed   in  equation    (6)  c.nd   in  \vhr.t    follo\vs  thct  perfect  buoyc.ncy 
exists  t]ixoughout  the  entire  depth  o-f  the    foundation.   This    is   only  true  \vhen  tlve 
•  :  •  ter  c-n  r.ct  freely  tlrou^i  the  mud  rnd  s^.ixL  rnc1    Ir.ve  perfect  access  to  r.ll 
joints,    In  neither  of  its  conditionc   cr.n  this    assumption  be    flilly  realized  in 
practice.  Further  in  equation   (6)   f  has  been  used  instead  of  m  because  mud  ^ 

certainly  cannot   flov-   into  fee  v.:a£,  onr  y  wher  eas  w~ter   as  already   strted  n£.y.    For 
the  regaining  blocks     f  will  be  used  instead  of  s.     Asa  in:  - 

t5   =    J  Y/4.  o    ..................    (7) 

]       cpi   -  ch5   (vji   -  |) 

The  total  pressure   on   the    rock   surface   is    :  ¥5  =  ¥5   +  CtgShgwj  -  kctgShgf 
If  water  gets  freely  into  the  bed  joint,  k  =  1,  and 

W6   -  V/5   +  ctG-^hsv/!   -  Ct62h5f 
If  no  water  gets   in  the   rock  bed  joint  k  =  0  and 

W6   =  175  -i-  ct52h6wi  =  W  +^cthv/o 

Where  Tcthw  equals  the    total  \veight   of  H:.e  pier,   no  water  gettir^;    into  any  joint. 
The   veight  of  the    totrl  cr.  terial  displrced  above   bedrock  by  the  pier    is:- 


225 


M  =  c    (ti2*(hi-h)    +  t22h£   +  tsh3    ]    f  +  ct42h4m  -t-  c   ^^hs  +  t62^6   \   s, 
The  abnormal  pressure  on  rod:  bottom  is,   vith  no  buoyr.nt  reduction:  - 

P  =  Wg  -  M  =  W  +  Fcthw  -  M  '  Ct62pk        .......   ..........    (8) 

P0    is  the  greatest  allowable  pressure   intensity  on  bedrock.    If  pQ^  pi,  use  p-^ 
in  equation   (8).  Neglecting  tha  inequality  in  equation  (8): 


t6   =A'       W  -t-gcth-.v  -  M  .......    ..........      (9) 

V  cp0 

If  buoyant  action  effects  any  or  all  joints  proper  reduction  mud&t  be 
made  in  the  effective  v/  eights   of  the  respective  terms  in£ctlro.  of  equation   (S), 

ABDITIOML  BLFERMCES 

1.   H.  L.Wiley,     The  Sinking  of  the   Piers  for   the  Grand  Truck  Pacific 
Bridge  at  Fort  Willion,   Ontario,  Canada;   Trans.    Am.   Soc.    C,E,  ,  Vol.62,  p. 


2.  O.LaBrodie,  Mrsonry  Drin  Formulas;   Columbia  University  School  of  Mines 
Quarterly,  Vol.29,  p.  241;  Vol.31,  p.  145. 

3.  H,  Chatley;    Stresses  in  Masonry. 

4.  C.S>G-ov/en   -  The   Changes  at  the  New  Croton  Bam;   Trans.  Am.   Soc.  C.E, 
Vol.56,  p.  32. 

5.  Col.    Harrison  and  S.  H.  Woodv/ard  ,   Lake  Cheesman  Drm  rnd  Reservoir, 
Trans.  A;-n.    Soc.    C,E.-,  Vol.53,   p.  89  = 

6.  L.Jorgensen;  Arch  Dam  Design;   The   Constpjit  Angle  Arch  Dam;   Eng.   Hews, 
Vol.68,  p.  155;   The   Influence  of  Poisson's  Batio  on  Stresses  in  Arch  Dams,  Eng. 
Hews,  Vol.68,  p.  208. 

7o   H.LKDworth,   G-eology   of  D?JII  Trenches;  Eng.  lews,  Vol.67,  p.  476; 
Asso.    of  Water  Engineers   of  G-t.    Britain,    1911. 

8.   G.YoWisner   rnd  E.T.  Wheeler,   Investigation  of  Stresses  in  High  Masonry 
Dams  of  Short  Spans,   Eng.  Ee\vs,  Vol.54,  p.  141. 


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